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[MachineBasicBlock] Take advantage of the partially dead information. 

Thanks to that information we wouldn't lie on a register being live whereas it
is not.

llvm-svn: 267622
This commit is contained in:
Quentin Colombet 2016-04-26 23:14:29 +00:00
parent 3f19245015
commit 08e79990a0
2 changed files with 10 additions and 4 deletions
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11
llvm/lib/CodeGen/MachineBasicBlock.cpp
View File

@ -1208,8 +1208,15 @@ MachineBasicBlock::computeRegisterLiveness(const TargetRegisterInfo *TRI,
if (Info.DeadDef)
return LQR_Dead;
// Register is (at least partially) live after a def.
if (Info.Defined)
return LQR_Live;
if (Info.Defined) {
if (!Info.PartialDeadDef)
return LQR_Live;
// As soon as we saw a partial definition (dead or not),
// we cannot tell if the value is partial live without
// tracking the lanemasks. We are not going to do this,
// so fall back on the remaining of the analysis.
break;
}
// Register is dead after a full kill or clobber and no def.
if (Info.Killed || Info.Clobbered)
return LQR_Dead;

3
llvm/test/CodeGen/X86/cmpxchg-clobber-flags.ll
View File

@ -167,11 +167,10 @@ define i32 @test_feed_cmov(i32* %addr, i32 %desired, i32 %new) {
; x8664-sahf-LABEL: test_feed_cmov:
; x8664-sahf: cmpxchgl
; x8664-sahf: pushq %rax
; RAX is dead, do not push or pop it.
; x8664-sahf-NEXT: seto %al
; x8664-sahf-NEXT: lahf
; x8664-sahf-NEXT: movq %rax, [[FLAGS:%.*]]
; x8664-sahf-NEXT: popq %rax
; x8664-sahf-NEXT: callq foo
; x8664-sahf-NEXT: pushq %rax
; x8664-sahf-NEXT: movq [[FLAGS]], %rax