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a1532bc283
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26299 91177308-0d34-0410-b5e6-96231b3b80d8
82 lines
2.1 KiB
Plaintext
82 lines
2.1 KiB
Plaintext
Target Independent Opportunities:
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===-------------------------------------------------------------------------===
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FreeBench/mason contains code like this:
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static p_type m0u(p_type p) {
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int m[]={0, 8, 1, 2, 16, 5, 13, 7, 14, 9, 3, 4, 11, 12, 15, 10, 17, 6};
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p_type pu;
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pu.a = m[p.a];
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pu.b = m[p.b];
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pu.c = m[p.c];
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return pu;
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}
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We currently compile this into a memcpy from a static array into 'm', then
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a bunch of loads from m. It would be better to avoid the memcpy and just do
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loads from the static array.
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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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//===---------------------------------------------------------------------===//
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DAG combine this into mul A, 8:
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int %test(int %A) {
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%B = mul int %A, 8 ;; shift
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%C = add int %B, 7 ;; dead, no demanded bits.
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%D = and int %C, -8 ;; dead once add is gone.
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ret int %D
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}
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This sort of thing occurs in the alloca lowering code and other places that
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are generating alignment of an already aligned value.
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//===---------------------------------------------------------------------===//
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Turn this into a signed shift right in instcombine:
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int f(unsigned x) {
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return x >> 31 ? -1 : 0;
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}
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25600
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http://gcc.gnu.org/ml/gcc-patches/2006-02/msg01492.html
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