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improve heuristics to find the 'and' corresponding to 'tst' to also catch opportunities on thumb2

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added some doxygen on the way

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115033 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Gabor Greif 2010-09-29 10:12:08 +00:00
parent afa4163afa
commit 05642a3eba
2 changed files with 32 additions and 16 deletions
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28
lib/Target/ARM/ARMBaseInstrInfo.cpp
View File

@ -1433,16 +1433,29 @@ AnalyzeCompare(const MachineInstr *MI, unsigned &SrcReg, int &CmpMask,
return false;
}
static bool isSuitableForMask(const MachineInstr &MI, unsigned SrcReg,
/// isSuitableForMask - Identify a suitable 'and' instruction that
/// operates on the given source register and applies the same mask
/// as a 'tst' instruction. Provide a limited look-through for copies.
/// When successful, MI will hold the found instruction.
static bool isSuitableForMask(MachineInstr *&MI, unsigned SrcReg,
int CmpMask, bool CommonUse) {
switch (MI.getOpcode()) {
switch (MI->getOpcode()) {
case ARM::ANDri:
case ARM::t2ANDri:
if (CmpMask != MI.getOperand(2).getImm())
if (CmpMask != MI->getOperand(2).getImm())
return false;
if (SrcReg == MI.getOperand(CommonUse ? 1 : 0).getReg())
if (SrcReg == MI->getOperand(CommonUse ? 1 : 0).getReg())
return true;
break;
case ARM::COPY: {
// Walk down one instruction which is potentially an 'and'.
const MachineInstr &Copy = *MI;
MachineBasicBlock::iterator AND(next(MachineBasicBlock::iterator(MI)));
if (AND == MI->getParent()->end()) return false;
MI = AND;
return isSuitableForMask(MI, Copy.getOperand(0).getReg(),
CmpMask, true);
}
}
return false;
@ -1467,16 +1480,15 @@ OptimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, int CmpMask,
// Masked compares sometimes use the same register as the corresponding 'and'.
if (CmpMask != ~0) {
if (!isSuitableForMask(*MI, SrcReg, CmpMask, false)) {
if (!isSuitableForMask(MI, SrcReg, CmpMask, false)) {
MI = 0;
for (MachineRegisterInfo::use_iterator UI = MRI.use_begin(SrcReg),
UE = MRI.use_end(); UI != UE; ++UI) {
if (UI->getParent() != CmpInstr->getParent()) continue;
MachineInstr &PotentialAND = *UI;
MachineInstr *PotentialAND = &*UI;
if (!isSuitableForMask(PotentialAND, SrcReg, CmpMask, true))
continue;
SrcReg = PotentialAND.getOperand(0).getReg();
MI = &PotentialAND;
MI = PotentialAND;
break;
}
if (!MI) return false;

20
test/CodeGen/ARM/arm-and-tst-peephole.ll
View File

@ -1,5 +1,6 @@
; RUN: llc < %s -mtriple=arm-apple-darwin | FileCheck %s
; RUN: llc < %s -mtriple=thumbv6-apple-darwin | FileCheck -check-prefix=T2 %s
; RUN: llc < %s -march=arm | FileCheck %s
; RUN: llc < %s -march=thumb | FileCheck -check-prefix=THUMB %s
; RUN: llc < %s -march=thumb -mattr=+thumb2 | FileCheck -check-prefix=T2 %s
%struct.Foo = type { i8* }
@ -18,13 +19,16 @@ tailrecurse: ; preds = %sw.bb, %entry
%0 = ptrtoint i8* %tmp2 to i32
; CHECK: ands r12, r12, #3
; CHECK-NEXT: beq LBB0_2
; CHECK-NEXT: beq .LBB0_2
; T2: movs r5, #3
; T2-NEXT: mov r6, r4
; T2-NEXT: ands r6, r5
; T2-NEXT: tst r4, r5
; T2-NEXT: beq LBB0_3
; THUMB: movs r5, #3
; THUMB-NEXT: mov r6, r4
; THUMB-NEXT: ands r6, r5
; THUMB-NEXT: tst r4, r5
; THUMB-NEXT: beq .LBB0_3
; T2: ands r12, r12, #3
; T2-NEXT: beq .LBB0_3
%and = and i32 %0, 3
%tst = icmp eq i32 %and, 0