mirror of
https://github.com/c64scene-ar/llvm-6502.git
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a11deb0392
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47803 91177308-0d34-0410-b5e6-96231b3b80d8
708 lines
21 KiB
Plaintext
708 lines
21 KiB
Plaintext
Target Independent Opportunities:
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//===---------------------------------------------------------------------===//
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We should make the various target's "IMPLICIT_DEF" instructions be a single
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target-independent opcode like TargetInstrInfo::INLINEASM. This would allow
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us to eliminate the TargetInstrDesc::isImplicitDef() method, and would allow
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us to avoid having to define this for every target for every register class.
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//===---------------------------------------------------------------------===//
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With the recent changes to make the implicit def/use set explicit in
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machineinstrs, we should change the target descriptions for 'call' instructions
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so that the .td files don't list all the call-clobbered registers as implicit
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defs. Instead, these should be added by the code generator (e.g. on the dag).
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This has a number of uses:
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1. PPC32/64 and X86 32/64 can avoid having multiple copies of call instructions
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for their different impdef sets.
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2. Targets with multiple calling convs (e.g. x86) which have different clobber
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sets don't need copies of call instructions.
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3. 'Interprocedural register allocation' can be done to reduce the clobber sets
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of calls.
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//===---------------------------------------------------------------------===//
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Make the PPC branch selector target independant
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//===---------------------------------------------------------------------===//
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Get the C front-end to expand hypot(x,y) -> llvm.sqrt(x*x+y*y) when errno and
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precision don't matter (ffastmath). Misc/mandel will like this. :)
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//===---------------------------------------------------------------------===//
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Solve this DAG isel folding deficiency:
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int X, Y;
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void fn1(void)
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{
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X = X | (Y << 3);
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}
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compiles to
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fn1:
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movl Y, %eax
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shll $3, %eax
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orl X, %eax
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movl %eax, X
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ret
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The problem is the store's chain operand is not the load X but rather
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a TokenFactor of the load X and load Y, which prevents the folding.
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There are two ways to fix this:
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1. The dag combiner can start using alias analysis to realize that y/x
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don't alias, making the store to X not dependent on the load from Y.
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2. The generated isel could be made smarter in the case it can't
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disambiguate the pointers.
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Number 1 is the preferred solution.
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This has been "fixed" by a TableGen hack. But that is a short term workaround
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which will be removed once the proper fix is made.
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//===---------------------------------------------------------------------===//
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On targets with expensive 64-bit multiply, we could LSR this:
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for (i = ...; ++i) {
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x = 1ULL << i;
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into:
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long long tmp = 1;
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for (i = ...; ++i, tmp+=tmp)
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x = tmp;
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This would be a win on ppc32, but not x86 or ppc64.
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//===---------------------------------------------------------------------===//
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Shrink: (setlt (loadi32 P), 0) -> (setlt (loadi8 Phi), 0)
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//===---------------------------------------------------------------------===//
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Reassociate should turn: X*X*X*X -> t=(X*X) (t*t) to eliminate a multiply.
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//===---------------------------------------------------------------------===//
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Interesting? testcase for add/shift/mul reassoc:
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int bar(int x, int y) {
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return x*x*x+y+x*x*x*x*x*y*y*y*y;
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}
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int foo(int z, int n) {
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return bar(z, n) + bar(2*z, 2*n);
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}
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Reassociate should handle the example in GCC PR16157.
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//===---------------------------------------------------------------------===//
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These two functions should generate the same code on big-endian systems:
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int g(int *j,int *l) { return memcmp(j,l,4); }
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int h(int *j, int *l) { return *j - *l; }
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this could be done in SelectionDAGISel.cpp, along with other special cases,
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for 1,2,4,8 bytes.
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//===---------------------------------------------------------------------===//
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It would be nice to revert this patch:
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http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20060213/031986.html
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And teach the dag combiner enough to simplify the code expanded before
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legalize. It seems plausible that this knowledge would let it simplify other
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stuff too.
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//===---------------------------------------------------------------------===//
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For vector types, TargetData.cpp::getTypeInfo() returns alignment that is equal
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to the type size. It works but can be overly conservative as the alignment of
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specific vector types are target dependent.
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//===---------------------------------------------------------------------===//
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We should add 'unaligned load/store' nodes, and produce them from code like
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this:
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v4sf example(float *P) {
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return (v4sf){P[0], P[1], P[2], P[3] };
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}
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//===---------------------------------------------------------------------===//
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Add support for conditional increments, and other related patterns. Instead
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of:
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movl 136(%esp), %eax
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cmpl $0, %eax
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je LBB16_2 #cond_next
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LBB16_1: #cond_true
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incl _foo
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LBB16_2: #cond_next
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emit:
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movl _foo, %eax
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cmpl $1, %edi
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sbbl $-1, %eax
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movl %eax, _foo
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//===---------------------------------------------------------------------===//
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Combine: a = sin(x), b = cos(x) into a,b = sincos(x).
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Expand these to calls of sin/cos and stores:
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double sincos(double x, double *sin, double *cos);
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float sincosf(float x, float *sin, float *cos);
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long double sincosl(long double x, long double *sin, long double *cos);
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Doing so could allow SROA of the destination pointers. See also:
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17687
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//===---------------------------------------------------------------------===//
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Scalar Repl cannot currently promote this testcase to 'ret long cst':
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%struct.X = type { i32, i32 }
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%struct.Y = type { %struct.X }
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define i64 @bar() {
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%retval = alloca %struct.Y, align 8
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%tmp12 = getelementptr %struct.Y* %retval, i32 0, i32 0, i32 0
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store i32 0, i32* %tmp12
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%tmp15 = getelementptr %struct.Y* %retval, i32 0, i32 0, i32 1
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store i32 1, i32* %tmp15
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%retval.upgrd.1 = bitcast %struct.Y* %retval to i64*
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%retval.upgrd.2 = load i64* %retval.upgrd.1
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ret i64 %retval.upgrd.2
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}
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it should be extended to do so.
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//===---------------------------------------------------------------------===//
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-scalarrepl should promote this to be a vector scalar.
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%struct..0anon = type { <4 x float> }
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define void @test1(<4 x float> %V, float* %P) {
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%u = alloca %struct..0anon, align 16
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%tmp = getelementptr %struct..0anon* %u, i32 0, i32 0
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store <4 x float> %V, <4 x float>* %tmp
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%tmp1 = bitcast %struct..0anon* %u to [4 x float]*
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%tmp.upgrd.1 = getelementptr [4 x float]* %tmp1, i32 0, i32 1
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%tmp.upgrd.2 = load float* %tmp.upgrd.1
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%tmp3 = mul float %tmp.upgrd.2, 2.000000e+00
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store float %tmp3, float* %P
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ret void
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}
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//===---------------------------------------------------------------------===//
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Turn this into a single byte store with no load (the other 3 bytes are
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unmodified):
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void %test(uint* %P) {
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%tmp = load uint* %P
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%tmp14 = or uint %tmp, 3305111552
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%tmp15 = and uint %tmp14, 3321888767
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store uint %tmp15, uint* %P
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ret void
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}
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//===---------------------------------------------------------------------===//
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dag/inst combine "clz(x)>>5 -> x==0" for 32-bit x.
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Compile:
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int bar(int x)
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{
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int t = __builtin_clz(x);
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return -(t>>5);
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}
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to:
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_bar: addic r3,r3,-1
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subfe r3,r3,r3
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blr
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//===---------------------------------------------------------------------===//
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Legalize should lower ctlz like this:
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ctlz(x) = popcnt((x-1) & ~x)
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on targets that have popcnt but not ctlz. itanium, what else?
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//===---------------------------------------------------------------------===//
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quantum_sigma_x in 462.libquantum contains the following loop:
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for(i=0; i<reg->size; i++)
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{
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/* Flip the target bit of each basis state */
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reg->node[i].state ^= ((MAX_UNSIGNED) 1 << target);
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}
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Where MAX_UNSIGNED/state is a 64-bit int. On a 32-bit platform it would be just
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so cool to turn it into something like:
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long long Res = ((MAX_UNSIGNED) 1 << target);
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if (target < 32) {
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for(i=0; i<reg->size; i++)
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reg->node[i].state ^= Res & 0xFFFFFFFFULL;
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} else {
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for(i=0; i<reg->size; i++)
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reg->node[i].state ^= Res & 0xFFFFFFFF00000000ULL
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}
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... which would only do one 32-bit XOR per loop iteration instead of two.
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It would also be nice to recognize the reg->size doesn't alias reg->node[i], but
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alas...
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//===---------------------------------------------------------------------===//
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This isn't recognized as bswap by instcombine:
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unsigned int swap_32(unsigned int v) {
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v = ((v & 0x00ff00ffU) << 8) | ((v & 0xff00ff00U) >> 8);
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v = ((v & 0x0000ffffU) << 16) | ((v & 0xffff0000U) >> 16);
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return v;
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}
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Nor is this (yes, it really is bswap):
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unsigned long reverse(unsigned v) {
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unsigned t;
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t = v ^ ((v << 16) | (v >> 16));
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t &= ~0xff0000;
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v = (v << 24) | (v >> 8);
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return v ^ (t >> 8);
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}
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//===---------------------------------------------------------------------===//
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These should turn into single 16-bit (unaligned?) loads on little/big endian
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processors.
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unsigned short read_16_le(const unsigned char *adr) {
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return adr[0] | (adr[1] << 8);
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}
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unsigned short read_16_be(const unsigned char *adr) {
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return (adr[0] << 8) | adr[1];
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}
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//===---------------------------------------------------------------------===//
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-instcombine should handle this transform:
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icmp pred (sdiv X / C1 ), C2
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when X, C1, and C2 are unsigned. Similarly for udiv and signed operands.
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Currently InstCombine avoids this transform but will do it when the signs of
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the operands and the sign of the divide match. See the FIXME in
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InstructionCombining.cpp in the visitSetCondInst method after the switch case
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for Instruction::UDiv (around line 4447) for more details.
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The SingleSource/Benchmarks/Shootout-C++/hash and hash2 tests have examples of
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this construct.
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//===---------------------------------------------------------------------===//
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Instcombine misses several of these cases (see the testcase in the patch):
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http://gcc.gnu.org/ml/gcc-patches/2006-10/msg01519.html
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//===---------------------------------------------------------------------===//
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viterbi speeds up *significantly* if the various "history" related copy loops
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are turned into memcpy calls at the source level. We need a "loops to memcpy"
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pass.
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//===---------------------------------------------------------------------===//
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Consider:
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typedef unsigned U32;
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typedef unsigned long long U64;
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int test (U32 *inst, U64 *regs) {
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U64 effective_addr2;
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U32 temp = *inst;
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int r1 = (temp >> 20) & 0xf;
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int b2 = (temp >> 16) & 0xf;
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effective_addr2 = temp & 0xfff;
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if (b2) effective_addr2 += regs[b2];
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b2 = (temp >> 12) & 0xf;
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if (b2) effective_addr2 += regs[b2];
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effective_addr2 &= regs[4];
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if ((effective_addr2 & 3) == 0)
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return 1;
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return 0;
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}
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Note that only the low 2 bits of effective_addr2 are used. On 32-bit systems,
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we don't eliminate the computation of the top half of effective_addr2 because
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we don't have whole-function selection dags. On x86, this means we use one
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extra register for the function when effective_addr2 is declared as U64 than
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when it is declared U32.
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//===---------------------------------------------------------------------===//
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Promote for i32 bswap can use i64 bswap + shr. Useful on targets with 64-bit
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regs and bswap, like itanium.
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//===---------------------------------------------------------------------===//
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LSR should know what GPR types a target has. This code:
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volatile short X, Y; // globals
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void foo(int N) {
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int i;
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for (i = 0; i < N; i++) { X = i; Y = i*4; }
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}
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produces two identical IV's (after promotion) on PPC/ARM:
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LBB1_1: @bb.preheader
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mov r3, #0
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mov r2, r3
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mov r1, r3
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LBB1_2: @bb
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ldr r12, LCPI1_0
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ldr r12, [r12]
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strh r2, [r12]
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ldr r12, LCPI1_1
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ldr r12, [r12]
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strh r3, [r12]
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add r1, r1, #1 <- [0,+,1]
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add r3, r3, #4
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add r2, r2, #1 <- [0,+,1]
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cmp r1, r0
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bne LBB1_2 @bb
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//===---------------------------------------------------------------------===//
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Tail call elim should be more aggressive, checking to see if the call is
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followed by an uncond branch to an exit block.
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; This testcase is due to tail-duplication not wanting to copy the return
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; instruction into the terminating blocks because there was other code
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; optimized out of the function after the taildup happened.
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; RUN: llvm-as < %s | opt -tailcallelim | llvm-dis | not grep call
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define i32 @t4(i32 %a) {
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entry:
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%tmp.1 = and i32 %a, 1 ; <i32> [#uses=1]
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%tmp.2 = icmp ne i32 %tmp.1, 0 ; <i1> [#uses=1]
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br i1 %tmp.2, label %then.0, label %else.0
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then.0: ; preds = %entry
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%tmp.5 = add i32 %a, -1 ; <i32> [#uses=1]
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%tmp.3 = call i32 @t4( i32 %tmp.5 ) ; <i32> [#uses=1]
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br label %return
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else.0: ; preds = %entry
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%tmp.7 = icmp ne i32 %a, 0 ; <i1> [#uses=1]
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br i1 %tmp.7, label %then.1, label %return
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then.1: ; preds = %else.0
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%tmp.11 = add i32 %a, -2 ; <i32> [#uses=1]
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%tmp.9 = call i32 @t4( i32 %tmp.11 ) ; <i32> [#uses=1]
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br label %return
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return: ; preds = %then.1, %else.0, %then.0
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%result.0 = phi i32 [ 0, %else.0 ], [ %tmp.3, %then.0 ],
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[ %tmp.9, %then.1 ]
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ret i32 %result.0
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}
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//===---------------------------------------------------------------------===//
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Tail recursion elimination is not transforming this function, because it is
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returning n, which fails the isDynamicConstant check in the accumulator
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recursion checks.
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long long fib(const long long n) {
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switch(n) {
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case 0:
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case 1:
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return n;
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default:
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return fib(n-1) + fib(n-2);
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}
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}
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//===---------------------------------------------------------------------===//
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Argument promotion should promote arguments for recursive functions, like
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this:
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; RUN: llvm-as < %s | opt -argpromotion | llvm-dis | grep x.val
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define internal i32 @foo(i32* %x) {
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entry:
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%tmp = load i32* %x ; <i32> [#uses=0]
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%tmp.foo = call i32 @foo( i32* %x ) ; <i32> [#uses=1]
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ret i32 %tmp.foo
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}
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define i32 @bar(i32* %x) {
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entry:
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%tmp3 = call i32 @foo( i32* %x ) ; <i32> [#uses=1]
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ret i32 %tmp3
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}
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//===---------------------------------------------------------------------===//
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"basicaa" should know how to look through "or" instructions that act like add
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instructions. For example in this code, the x*4+1 is turned into x*4 | 1, and
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basicaa can't analyze the array subscript, leading to duplicated loads in the
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generated code:
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void test(int X, int Y, int a[]) {
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int i;
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for (i=2; i<1000; i+=4) {
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a[i+0] = a[i-1+0]*a[i-2+0];
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a[i+1] = a[i-1+1]*a[i-2+1];
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a[i+2] = a[i-1+2]*a[i-2+2];
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a[i+3] = a[i-1+3]*a[i-2+3];
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}
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}
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//===---------------------------------------------------------------------===//
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We should investigate an instruction sinking pass. Consider this silly
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example in pic mode:
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#include <assert.h>
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void foo(int x) {
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assert(x);
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//...
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}
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we compile this to:
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_foo:
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subl $28, %esp
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call "L1$pb"
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"L1$pb":
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popl %eax
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cmpl $0, 32(%esp)
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je LBB1_2 # cond_true
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LBB1_1: # return
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# ...
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addl $28, %esp
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ret
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LBB1_2: # cond_true
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...
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The PIC base computation (call+popl) is only used on one path through the
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code, but is currently always computed in the entry block. It would be
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better to sink the picbase computation down into the block for the
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assertion, as it is the only one that uses it. This happens for a lot of
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code with early outs.
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Another example is loads of arguments, which are usually emitted into the
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entry block on targets like x86. If not used in all paths through a
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function, they should be sunk into the ones that do.
|
|
|
|
In this case, whole-function-isel would also handle this.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Investigate lowering of sparse switch statements into perfect hash tables:
|
|
http://burtleburtle.net/bob/hash/perfect.html
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We should turn things like "load+fabs+store" and "load+fneg+store" into the
|
|
corresponding integer operations. On a yonah, this loop:
|
|
|
|
double a[256];
|
|
void foo() {
|
|
int i, b;
|
|
for (b = 0; b < 10000000; b++)
|
|
for (i = 0; i < 256; i++)
|
|
a[i] = -a[i];
|
|
}
|
|
|
|
is twice as slow as this loop:
|
|
|
|
long long a[256];
|
|
void foo() {
|
|
int i, b;
|
|
for (b = 0; b < 10000000; b++)
|
|
for (i = 0; i < 256; i++)
|
|
a[i] ^= (1ULL << 63);
|
|
}
|
|
|
|
and I suspect other processors are similar. On X86 in particular this is a
|
|
big win because doing this with integers allows the use of read/modify/write
|
|
instructions.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
DAG Combiner should try to combine small loads into larger loads when
|
|
profitable. For example, we compile this C++ example:
|
|
|
|
struct THotKey { short Key; bool Control; bool Shift; bool Alt; };
|
|
extern THotKey m_HotKey;
|
|
THotKey GetHotKey () { return m_HotKey; }
|
|
|
|
into (-O3 -fno-exceptions -static -fomit-frame-pointer):
|
|
|
|
__Z9GetHotKeyv:
|
|
pushl %esi
|
|
movl 8(%esp), %eax
|
|
movb _m_HotKey+3, %cl
|
|
movb _m_HotKey+4, %dl
|
|
movb _m_HotKey+2, %ch
|
|
movw _m_HotKey, %si
|
|
movw %si, (%eax)
|
|
movb %ch, 2(%eax)
|
|
movb %cl, 3(%eax)
|
|
movb %dl, 4(%eax)
|
|
popl %esi
|
|
ret $4
|
|
|
|
GCC produces:
|
|
|
|
__Z9GetHotKeyv:
|
|
movl _m_HotKey, %edx
|
|
movl 4(%esp), %eax
|
|
movl %edx, (%eax)
|
|
movzwl _m_HotKey+4, %edx
|
|
movw %dx, 4(%eax)
|
|
ret $4
|
|
|
|
The LLVM IR contains the needed alignment info, so we should be able to
|
|
merge the loads and stores into 4-byte loads:
|
|
|
|
%struct.THotKey = type { i16, i8, i8, i8 }
|
|
define void @_Z9GetHotKeyv(%struct.THotKey* sret %agg.result) nounwind {
|
|
...
|
|
%tmp2 = load i16* getelementptr (@m_HotKey, i32 0, i32 0), align 8
|
|
%tmp5 = load i8* getelementptr (@m_HotKey, i32 0, i32 1), align 2
|
|
%tmp8 = load i8* getelementptr (@m_HotKey, i32 0, i32 2), align 1
|
|
%tmp11 = load i8* getelementptr (@m_HotKey, i32 0, i32 3), align 2
|
|
|
|
Alternatively, we should use a small amount of base-offset alias analysis
|
|
to make it so the scheduler doesn't need to hold all the loads in regs at
|
|
once.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We should extend parameter attributes to capture more information about
|
|
pointer parameters for alias analysis. Some ideas:
|
|
|
|
1. Add a "nocapture" attribute, which indicates that the callee does not store
|
|
the address of the parameter into a global or any other memory location
|
|
visible to the callee. This can be used to make basicaa and other analyses
|
|
more powerful. It is true for things like memcpy, strcat, and many other
|
|
things, including structs passed by value, most C++ references, etc.
|
|
2. Generalize readonly to be set on parameters. This is important mod/ref
|
|
info for the function, which is important for basicaa and others. It can
|
|
also be used by the inliner to avoid inserting a memcpy for byval
|
|
arguments when the function is inlined.
|
|
|
|
These functions can be inferred by various analysis passes such as the
|
|
globalsmodrefaa pass. Note that getting #2 right is actually really tricky.
|
|
Consider this code:
|
|
|
|
struct S; S G;
|
|
void caller(S byvalarg) { G.field = 1; ... }
|
|
void callee() { caller(G); }
|
|
|
|
The fact that the caller does not modify byval arg is not enough, we need
|
|
to know that it doesn't modify G either. This is very tricky.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
We should add an FRINT node to the DAG to model targets that have legal
|
|
implementations of ceil/floor/rint.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
This GCC bug: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34043
|
|
contains a testcase that compiles down to:
|
|
|
|
%struct.XMM128 = type { <4 x float> }
|
|
..
|
|
%src = alloca %struct.XMM128
|
|
..
|
|
%tmp6263 = bitcast %struct.XMM128* %src to <2 x i64>*
|
|
%tmp65 = getelementptr %struct.XMM128* %src, i32 0, i32 0
|
|
store <2 x i64> %tmp5899, <2 x i64>* %tmp6263, align 16
|
|
%tmp66 = load <4 x float>* %tmp65, align 16
|
|
%tmp71 = add <4 x float> %tmp66, %tmp66
|
|
|
|
If the mid-level optimizer turned the bitcast of pointer + store of tmp5899
|
|
into a bitcast of the vector value and a store to the pointer, then the
|
|
store->load could be easily removed.
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
Consider:
|
|
|
|
int test() {
|
|
long long input[8] = {1,1,1,1,1,1,1,1};
|
|
foo(input);
|
|
}
|
|
|
|
We currently compile this into a memcpy from a global array since the
|
|
initializer is fairly large and not memset'able. This is good, but the memcpy
|
|
gets lowered to load/stores in the code generator. This is also ok, except
|
|
that the codegen lowering for memcpy doesn't handle the case when the source
|
|
is a constant global. This gives us atrocious code like this:
|
|
|
|
call "L1$pb"
|
|
"L1$pb":
|
|
popl %eax
|
|
movl _C.0.1444-"L1$pb"+32(%eax), %ecx
|
|
movl %ecx, 40(%esp)
|
|
movl _C.0.1444-"L1$pb"+20(%eax), %ecx
|
|
movl %ecx, 28(%esp)
|
|
movl _C.0.1444-"L1$pb"+36(%eax), %ecx
|
|
movl %ecx, 44(%esp)
|
|
movl _C.0.1444-"L1$pb"+44(%eax), %ecx
|
|
movl %ecx, 52(%esp)
|
|
movl _C.0.1444-"L1$pb"+40(%eax), %ecx
|
|
movl %ecx, 48(%esp)
|
|
movl _C.0.1444-"L1$pb"+12(%eax), %ecx
|
|
movl %ecx, 20(%esp)
|
|
movl _C.0.1444-"L1$pb"+4(%eax), %ecx
|
|
...
|
|
|
|
instead of:
|
|
movl $1, 16(%esp)
|
|
movl $0, 20(%esp)
|
|
movl $1, 24(%esp)
|
|
movl $0, 28(%esp)
|
|
movl $1, 32(%esp)
|
|
movl $0, 36(%esp)
|
|
...
|
|
|
|
//===---------------------------------------------------------------------===//
|
|
|
|
http://llvm.org/PR717:
|
|
|
|
The following code should compile into "ret int undef". Instead, LLVM
|
|
produces "ret int 0":
|
|
|
|
int f() {
|
|
int x = 4;
|
|
int y;
|
|
if (x == 3) y = 0;
|
|
return y;
|
|
}
|
|
|
|
//===---------------------------------------------------------------------===//
|