mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-11-14 13:07:31 +00:00
b86bd2cee2
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27168 91177308-0d34-0410-b5e6-96231b3b80d8
554 lines
15 KiB
Plaintext
554 lines
15 KiB
Plaintext
//===- README.txt - Notes for improving PowerPC-specific code gen ---------===//
|
|
|
|
TODO:
|
|
* gpr0 allocation
|
|
* implement do-loop -> bdnz transform
|
|
* implement powerpc-64 for darwin
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Support 'update' load/store instructions. These are cracked on the G5, but are
|
|
still a codesize win.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Teach the .td file to pattern match PPC::BR_COND to appropriate bc variant, so
|
|
we don't have to always run the branch selector for small functions.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
* Codegen this:
|
|
|
|
void test2(int X) {
|
|
if (X == 0x12345678) bar();
|
|
}
|
|
|
|
as:
|
|
|
|
xoris r0,r3,0x1234
|
|
cmplwi cr0,r0,0x5678
|
|
beq cr0,L6
|
|
|
|
not:
|
|
|
|
lis r2, 4660
|
|
ori r2, r2, 22136
|
|
cmpw cr0, r3, r2
|
|
bne .LBB_test2_2
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Lump the constant pool for each function into ONE pic object, and reference
|
|
pieces of it as offsets from the start. For functions like this (contrived
|
|
to have lots of constants obviously):
|
|
|
|
double X(double Y) { return (Y*1.23 + 4.512)*2.34 + 14.38; }
|
|
|
|
We generate:
|
|
|
|
_X:
|
|
lis r2, ha16(.CPI_X_0)
|
|
lfd f0, lo16(.CPI_X_0)(r2)
|
|
lis r2, ha16(.CPI_X_1)
|
|
lfd f2, lo16(.CPI_X_1)(r2)
|
|
fmadd f0, f1, f0, f2
|
|
lis r2, ha16(.CPI_X_2)
|
|
lfd f1, lo16(.CPI_X_2)(r2)
|
|
lis r2, ha16(.CPI_X_3)
|
|
lfd f2, lo16(.CPI_X_3)(r2)
|
|
fmadd f1, f0, f1, f2
|
|
blr
|
|
|
|
It would be better to materialize .CPI_X into a register, then use immediates
|
|
off of the register to avoid the lis's. This is even more important in PIC
|
|
mode.
|
|
|
|
Note that this (and the static variable version) is discussed here for GCC:
|
|
http://gcc.gnu.org/ml/gcc-patches/2006-02/msg00133.html
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
PIC Code Gen IPO optimization:
|
|
|
|
Squish small scalar globals together into a single global struct, allowing the
|
|
address of the struct to be CSE'd, avoiding PIC accesses (also reduces the size
|
|
of the GOT on targets with one).
|
|
|
|
Note that this is discussed here for GCC:
|
|
http://gcc.gnu.org/ml/gcc-patches/2006-02/msg00133.html
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Implement Newton-Rhapson method for improving estimate instructions to the
|
|
correct accuracy, and implementing divide as multiply by reciprocal when it has
|
|
more than one use. Itanium will want this too.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
#define ARRAY_LENGTH 16
|
|
|
|
union bitfield {
|
|
struct {
|
|
#ifndef __ppc__
|
|
unsigned int field0 : 6;
|
|
unsigned int field1 : 6;
|
|
unsigned int field2 : 6;
|
|
unsigned int field3 : 6;
|
|
unsigned int field4 : 3;
|
|
unsigned int field5 : 4;
|
|
unsigned int field6 : 1;
|
|
#else
|
|
unsigned int field6 : 1;
|
|
unsigned int field5 : 4;
|
|
unsigned int field4 : 3;
|
|
unsigned int field3 : 6;
|
|
unsigned int field2 : 6;
|
|
unsigned int field1 : 6;
|
|
unsigned int field0 : 6;
|
|
#endif
|
|
} bitfields, bits;
|
|
unsigned int u32All;
|
|
signed int i32All;
|
|
float f32All;
|
|
};
|
|
|
|
|
|
typedef struct program_t {
|
|
union bitfield array[ARRAY_LENGTH];
|
|
int size;
|
|
int loaded;
|
|
} program;
|
|
|
|
|
|
void AdjustBitfields(program* prog, unsigned int fmt1)
|
|
{
|
|
prog->array[0].bitfields.field0 = fmt1;
|
|
prog->array[0].bitfields.field1 = fmt1 + 1;
|
|
}
|
|
|
|
We currently generate:
|
|
|
|
_AdjustBitfields:
|
|
lwz r2, 0(r3)
|
|
addi r5, r4, 1
|
|
rlwinm r2, r2, 0, 0, 19
|
|
rlwinm r5, r5, 6, 20, 25
|
|
rlwimi r2, r4, 0, 26, 31
|
|
or r2, r2, r5
|
|
stw r2, 0(r3)
|
|
blr
|
|
|
|
We should teach someone that or (rlwimi, rlwinm) with disjoint masks can be
|
|
turned into rlwimi (rlwimi)
|
|
|
|
The better codegen would be:
|
|
|
|
_AdjustBitfields:
|
|
lwz r0,0(r3)
|
|
rlwinm r4,r4,0,0xff
|
|
rlwimi r0,r4,0,26,31
|
|
addi r4,r4,1
|
|
rlwimi r0,r4,6,20,25
|
|
stw r0,0(r3)
|
|
blr
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Compile this:
|
|
|
|
int %f1(int %a, int %b) {
|
|
%tmp.1 = and int %a, 15 ; <int> [#uses=1]
|
|
%tmp.3 = and int %b, 240 ; <int> [#uses=1]
|
|
%tmp.4 = or int %tmp.3, %tmp.1 ; <int> [#uses=1]
|
|
ret int %tmp.4
|
|
}
|
|
|
|
without a copy. We make this currently:
|
|
|
|
_f1:
|
|
rlwinm r2, r4, 0, 24, 27
|
|
rlwimi r2, r3, 0, 28, 31
|
|
or r3, r2, r2
|
|
blr
|
|
|
|
The two-addr pass or RA needs to learn when it is profitable to commute an
|
|
instruction to avoid a copy AFTER the 2-addr instruction. The 2-addr pass
|
|
currently only commutes to avoid inserting a copy BEFORE the two addr instr.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Compile offsets from allocas:
|
|
|
|
int *%test() {
|
|
%X = alloca { int, int }
|
|
%Y = getelementptr {int,int}* %X, int 0, uint 1
|
|
ret int* %Y
|
|
}
|
|
|
|
into a single add, not two:
|
|
|
|
_test:
|
|
addi r2, r1, -8
|
|
addi r3, r2, 4
|
|
blr
|
|
|
|
--> important for C++.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
int test3(int a, int b) { return (a < 0) ? a : 0; }
|
|
|
|
should be branch free code. LLVM is turning it into < 1 because of the RHS.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
No loads or stores of the constants should be needed:
|
|
|
|
struct foo { double X, Y; };
|
|
void xxx(struct foo F);
|
|
void bar() { struct foo R = { 1.0, 2.0 }; xxx(R); }
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Darwin Stub LICM optimization:
|
|
|
|
Loops like this:
|
|
|
|
for (...) bar();
|
|
|
|
Have to go through an indirect stub if bar is external or linkonce. It would
|
|
be better to compile it as:
|
|
|
|
fp = &bar;
|
|
for (...) fp();
|
|
|
|
which only computes the address of bar once (instead of each time through the
|
|
stub). This is Darwin specific and would have to be done in the code generator.
|
|
Probably not a win on x86.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
PowerPC i1/setcc stuff (depends on subreg stuff):
|
|
|
|
Check out the PPC code we get for 'compare' in this testcase:
|
|
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19672
|
|
|
|
oof. on top of not doing the logical crnand instead of (mfcr, mfcr,
|
|
invert, invert, or), we then have to compare it against zero instead of
|
|
using the value already in a CR!
|
|
|
|
that should be something like
|
|
cmpw cr7, r8, r5
|
|
cmpw cr0, r7, r3
|
|
crnand cr0, cr0, cr7
|
|
bne cr0, LBB_compare_4
|
|
|
|
instead of
|
|
cmpw cr7, r8, r5
|
|
cmpw cr0, r7, r3
|
|
mfcr r7, 1
|
|
mcrf cr7, cr0
|
|
mfcr r8, 1
|
|
rlwinm r7, r7, 30, 31, 31
|
|
rlwinm r8, r8, 30, 31, 31
|
|
xori r7, r7, 1
|
|
xori r8, r8, 1
|
|
addi r2, r2, 1
|
|
or r7, r8, r7
|
|
cmpwi cr0, r7, 0
|
|
bne cr0, LBB_compare_4 ; loopexit
|
|
|
|
FreeBench/mason has a basic block that looks like this:
|
|
|
|
%tmp.130 = seteq int %p.0__, 5 ; <bool> [#uses=1]
|
|
%tmp.134 = seteq int %p.1__, 6 ; <bool> [#uses=1]
|
|
%tmp.139 = seteq int %p.2__, 12 ; <bool> [#uses=1]
|
|
%tmp.144 = seteq int %p.3__, 13 ; <bool> [#uses=1]
|
|
%tmp.149 = seteq int %p.4__, 14 ; <bool> [#uses=1]
|
|
%tmp.154 = seteq int %p.5__, 15 ; <bool> [#uses=1]
|
|
%bothcond = and bool %tmp.134, %tmp.130 ; <bool> [#uses=1]
|
|
%bothcond123 = and bool %bothcond, %tmp.139 ; <bool>
|
|
%bothcond124 = and bool %bothcond123, %tmp.144 ; <bool>
|
|
%bothcond125 = and bool %bothcond124, %tmp.149 ; <bool>
|
|
%bothcond126 = and bool %bothcond125, %tmp.154 ; <bool>
|
|
br bool %bothcond126, label %shortcirc_next.5, label %else.0
|
|
|
|
This is a particularly important case where handling CRs better will help.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Simple IPO for argument passing, change:
|
|
void foo(int X, double Y, int Z) -> void foo(int X, int Z, double Y)
|
|
|
|
the Darwin ABI specifies that any integer arguments in the first 32 bytes worth
|
|
of arguments get assigned to r3 through r10. That is, if you have a function
|
|
foo(int, double, int) you get r3, f1, r6, since the 64 bit double ate up the
|
|
argument bytes for r4 and r5. The trick then would be to shuffle the argument
|
|
order for functions we can internalize so that the maximum number of
|
|
integers/pointers get passed in regs before you see any of the fp arguments.
|
|
|
|
Instead of implementing this, it would actually probably be easier to just
|
|
implement a PPC fastcc, where we could do whatever we wanted to the CC,
|
|
including having this work sanely.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Fix Darwin FP-In-Integer Registers ABI
|
|
|
|
Darwin passes doubles in structures in integer registers, which is very very
|
|
bad. Add something like a BIT_CONVERT to LLVM, then do an i-p transformation
|
|
that percolates these things out of functions.
|
|
|
|
Check out how horrible this is:
|
|
http://gcc.gnu.org/ml/gcc/2005-10/msg01036.html
|
|
|
|
This is an extension of "interprocedural CC unmunging" that can't be done with
|
|
just fastcc.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Generate lwbrx and other byteswapping load/store instructions when reasonable.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Compile this:
|
|
|
|
int foo(int a) {
|
|
int b = (a < 8);
|
|
if (b) {
|
|
return b * 3; // ignore the fact that this is always 3.
|
|
} else {
|
|
return 2;
|
|
}
|
|
}
|
|
|
|
into something not this:
|
|
|
|
_foo:
|
|
1) cmpwi cr7, r3, 8
|
|
mfcr r2, 1
|
|
rlwinm r2, r2, 29, 31, 31
|
|
1) cmpwi cr0, r3, 7
|
|
bgt cr0, LBB1_2 ; UnifiedReturnBlock
|
|
LBB1_1: ; then
|
|
rlwinm r2, r2, 0, 31, 31
|
|
mulli r3, r2, 3
|
|
blr
|
|
LBB1_2: ; UnifiedReturnBlock
|
|
li r3, 2
|
|
blr
|
|
|
|
In particular, the two compares (marked 1) could be shared by reversing one.
|
|
This could be done in the dag combiner, by swapping a BR_CC when a SETCC of the
|
|
same operands (but backwards) exists. In this case, this wouldn't save us
|
|
anything though, because the compares still wouldn't be shared.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
The legalizer should lower this:
|
|
|
|
bool %test(ulong %x) {
|
|
%tmp = setlt ulong %x, 4294967296
|
|
ret bool %tmp
|
|
}
|
|
|
|
into "if x.high == 0", not:
|
|
|
|
_test:
|
|
addi r2, r3, -1
|
|
cntlzw r2, r2
|
|
cntlzw r3, r3
|
|
srwi r2, r2, 5
|
|
srwi r4, r3, 5
|
|
li r3, 0
|
|
cmpwi cr0, r2, 0
|
|
bne cr0, LBB1_2 ;
|
|
LBB1_1:
|
|
or r3, r4, r4
|
|
LBB1_2:
|
|
blr
|
|
|
|
noticed in 2005-05-11-Popcount-ffs-fls.c.
|
|
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
We should custom expand setcc instead of pretending that we have it. That
|
|
would allow us to expose the access of the crbit after the mfcr, allowing
|
|
that access to be trivially folded into other ops. A simple example:
|
|
|
|
int foo(int a, int b) { return (a < b) << 4; }
|
|
|
|
compiles into:
|
|
|
|
_foo:
|
|
cmpw cr7, r3, r4
|
|
mfcr r2, 1
|
|
rlwinm r2, r2, 29, 31, 31
|
|
slwi r3, r2, 4
|
|
blr
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
Fold add and sub with constant into non-extern, non-weak addresses so this:
|
|
|
|
static int a;
|
|
void bar(int b) { a = b; }
|
|
void foo(unsigned char *c) {
|
|
*c = a;
|
|
}
|
|
|
|
So that
|
|
|
|
_foo:
|
|
lis r2, ha16(_a)
|
|
la r2, lo16(_a)(r2)
|
|
lbz r2, 3(r2)
|
|
stb r2, 0(r3)
|
|
blr
|
|
|
|
Becomes
|
|
|
|
_foo:
|
|
lis r2, ha16(_a+3)
|
|
lbz r2, lo16(_a+3)(r2)
|
|
stb r2, 0(r3)
|
|
blr
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
We generate really bad code for this:
|
|
|
|
int f(signed char *a, _Bool b, _Bool c) {
|
|
signed char t = 0;
|
|
if (b) t = *a;
|
|
if (c) *a = t;
|
|
}
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
This:
|
|
int test(unsigned *P) { return *P >> 24; }
|
|
|
|
Should compile to:
|
|
|
|
_test:
|
|
lbz r3,0(r3)
|
|
blr
|
|
|
|
not:
|
|
|
|
_test:
|
|
lwz r2, 0(r3)
|
|
srwi r3, r2, 24
|
|
blr
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
On the G5, logical CR operations are more expensive in their three
|
|
address form: ops that read/write the same register are half as expensive as
|
|
those that read from two registers that are different from their destination.
|
|
|
|
We should model this with two separate instructions. The isel should generate
|
|
the "two address" form of the instructions. When the register allocator
|
|
detects that it needs to insert a copy due to the two-addresness of the CR
|
|
logical op, it will invoke PPCInstrInfo::convertToThreeAddress. At this point
|
|
we can convert to the "three address" instruction, to save code space.
|
|
|
|
This only matters when we start generating cr logical ops.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
We should compile these two functions to the same thing:
|
|
|
|
#include <stdlib.h>
|
|
void f(int a, int b, int *P) {
|
|
*P = (a-b)>=0?(a-b):(b-a);
|
|
}
|
|
void g(int a, int b, int *P) {
|
|
*P = abs(a-b);
|
|
}
|
|
|
|
Further, they should compile to something better than:
|
|
|
|
_g:
|
|
subf r2, r4, r3
|
|
subfic r3, r2, 0
|
|
cmpwi cr0, r2, -1
|
|
bgt cr0, LBB2_2 ; entry
|
|
LBB2_1: ; entry
|
|
mr r2, r3
|
|
LBB2_2: ; entry
|
|
stw r2, 0(r5)
|
|
blr
|
|
|
|
GCC produces:
|
|
|
|
_g:
|
|
subf r4,r4,r3
|
|
srawi r2,r4,31
|
|
xor r0,r2,r4
|
|
subf r0,r2,r0
|
|
stw r0,0(r5)
|
|
blr
|
|
|
|
... which is much nicer.
|
|
|
|
This theoretically may help improve twolf slightly (used in dimbox.c:142?).
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
int foo(int N, int ***W, int **TK, int X) {
|
|
int t, i;
|
|
|
|
for (t = 0; t < N; ++t)
|
|
for (i = 0; i < 4; ++i)
|
|
W[t / X][i][t % X] = TK[i][t];
|
|
|
|
return 5;
|
|
}
|
|
|
|
We generate relatively atrocious code for this loop compared to gcc.
|
|
|
|
We could also strength reduce the rem and the div:
|
|
http://www.lcs.mit.edu/pubs/pdf/MIT-LCS-TM-600.pdf
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
float foo(float X) { return (int)(X); }
|
|
|
|
Currently produces:
|
|
|
|
_foo:
|
|
fctiwz f0, f1
|
|
stfd f0, -8(r1)
|
|
lwz r2, -4(r1)
|
|
extsw r2, r2
|
|
std r2, -16(r1)
|
|
lfd f0, -16(r1)
|
|
fcfid f0, f0
|
|
frsp f1, f0
|
|
blr
|
|
|
|
We could use a target dag combine to turn the lwz/extsw into an lwa when the
|
|
lwz has a single use. Since LWA is cracked anyway, this would be a codesize
|
|
win only.
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|
|
We generate ugly code for this:
|
|
|
|
void func(unsigned int *ret, float dx, float dy, float dz, float dw) {
|
|
unsigned code = 0;
|
|
if(dx < -dw) code |= 1;
|
|
if(dx > dw) code |= 2;
|
|
if(dy < -dw) code |= 4;
|
|
if(dy > dw) code |= 8;
|
|
if(dz < -dw) code |= 16;
|
|
if(dz > dw) code |= 32;
|
|
*ret = code;
|
|
}
|
|
|
|
===-------------------------------------------------------------------------===
|
|
|