6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2024-09-30 04:56:49 +00:00
Code Issues Projects Releases Wiki Activity

X86 Peephole: fix PR13475 in optimizeCompare.

Browse Source 
It is possible that an instruction can use and update EFLAGS.
When checking the safety, we should check the usage of EFLAGS first before
declaring it is safe to optimize due to the update.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160912 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren 2012-07-28 03:15:46 +00:00
parent 4b72ada1f4
commit 43d9ab1812
2 changed files with 23 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
lib/Target/X86/X86InstrInfo.cpp
View File

@ -3221,12 +3221,15 @@ optimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, unsigned SrcReg2,
MachineBasicBlock::iterator E = CmpInstr->getParent()->end();
for (++I; I != E; ++I) {
const MachineInstr &Instr = *I;
if (Instr.modifiesRegister(X86::EFLAGS, TRI)) {
bool ModifyEFLAGS = Instr.modifiesRegister(X86::EFLAGS, TRI);
bool UseEFLAGS = Instr.readsRegister(X86::EFLAGS, TRI);
// We should check the usage if this instruction uses and updates EFLAGS.
if (!UseEFLAGS && ModifyEFLAGS) {
// It is safe to remove CmpInstr if EFLAGS is updated again.
IsSafe = true;
break;
}
if (!Instr.readsRegister(X86::EFLAGS, TRI))
if (!UseEFLAGS && !ModifyEFLAGS)
continue;
// EFLAGS is used by this instruction.
@ -3281,7 +3284,8 @@ optimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, unsigned SrcReg2,
// instructions will be modified.
OpsToUpdate.push_back(std::make_pair(&*I, NewOpc));
}
if (Instr.killsRegister(X86::EFLAGS, TRI)) {
if (ModifyEFLAGS || Instr.killsRegister(X86::EFLAGS, TRI)) {
// It is safe to remove CmpInstr if EFLAGS is updated again or killed.
IsSafe = true;
break;
}

16
test/CodeGen/X86/jump_sign.ll
View File

@ -214,3 +214,19 @@ entry:
%add. = select i1 %cmp, i32 %add, i32 0
ret i32 %add.
}
; PR13475
; If we have sub a, b and cmp b, a and the result of cmp is used
; by sbb, we should not optimize cmp away.
define i32 @q(i32 %j.4, i32 %w, i32 %el) {
; CHECK: q:
; CHECK: sub
; CHECK: cmp
; CHECK-NEXT: sbb
%tmp532 = add i32 %j.4, %w
%tmp533 = icmp ugt i32 %tmp532, %el
%tmp534 = icmp ult i32 %w, %el
%or.cond = and i1 %tmp533, %tmp534
%tmp535 = sub i32 %el, %w
%j.5 = select i1 %or.cond, i32 %tmp535, i32 %j.4
ret i32 %j.5
}