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On x86-64, the 32-bit cmov doesn't actually clear the high 32-bit of

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its result if the condition is false.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81814 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-09-15 00:14:11 +00:00
parent e6798372ea
commit 907355caf8
2 changed files with 24 additions and 3 deletions
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8
lib/Target/X86/X86Instr64bit.td
View File

@ -387,13 +387,15 @@ def MOVZX64rm32 : I<0x8B, MRMSrcMem, (outs GR64:$dst), (ins i32mem:$src),
[(set GR64:$dst, (zextloadi64i32 addr:$src))]>;
// Any instruction that defines a 32-bit result leaves the high half of the
// register. Truncate can be lowered to EXTRACT_SUBREG, and CopyFromReg may
// be copying from a truncate, but any other 32-bit operation will zero-extend
// register. Truncate can be lowered to EXTRACT_SUBREG. CopyFromReg may
// be copying from a truncate. And x86's cmov doesn't do anything if the
// condition is false. But any other 32-bit operation will zero-extend
// up to 64 bits.
def def32 : PatLeaf<(i32 GR32:$src), [{
return N->getOpcode() != ISD::TRUNCATE &&
N->getOpcode() != TargetInstrInfo::EXTRACT_SUBREG &&
N->getOpcode() != ISD::CopyFromReg;
N->getOpcode() != ISD::CopyFromReg &&
N->getOpcode() != X86ISD::CMOV;
}]>;
// In the case of a 32-bit def that is known to implicitly zero-extend,

19
test/CodeGen/X86/cmov-zext.ll Normal file
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@ -0,0 +1,19 @@
; RUN: llc < %s -march=x86-64 | FileCheck %s
; x86's 32-bit cmov doesn't clobber the high 32 bits of the destination
; if the condition is false. An explicit zero-extend (movl) is needed
; after the cmov.
; CHECK: cmovne %edi, %esi
; CHECK-NEXT: movl %esi, %edi
declare void @bar(i64) nounwind
define void @foo(i64 %a, i64 %b, i1 %p) nounwind {
%c = trunc i64 %a to i32
%d = trunc i64 %b to i32
%e = select i1 %p, i32 %c, i32 %d
%f = zext i32 %e to i64
call void @bar(i64 %f)
ret void
}