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X86: Disable generation of rep;movsl when %esi is used as a base pointer.

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This happens when there is both stack realignment and a dynamic alloca in the
function. If we overwrite %esi (rep;movsl uses fixed registers) we'll lose the
base pointer and the next register spill will write into oblivion.

Fixes PR15249 and unbreaks firefox on i386/freebsd. Mozilla uses dynamic allocas
and freebsd a 4 byte stack alignment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175057 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2013-02-13 13:40:35 +00:00
parent 0f80f7bfd7
commit f09e02f01a
2 changed files with 26 additions and 0 deletions
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8
lib/Target/X86/X86SelectionDAGInfo.cpp
View File

@ -202,6 +202,14 @@ X86SelectionDAGInfo::EmitTargetCodeForMemcpy(SelectionDAG &DAG, DebugLoc dl,
SrcPtrInfo.getAddrSpace() >= 256)
return SDValue();
// ESI might be used as a base pointer, in that case we can't simply overwrite
// the register. Fall back to generic code.
const X86RegisterInfo *TRI =
static_cast<const X86RegisterInfo *>(DAG.getTarget().getRegisterInfo());
if (TRI->hasBasePointer(DAG.getMachineFunction()) &&
TRI->getBaseRegister() == X86::ESI)
return SDValue();
MVT AVT;
if (Align & 1)
AVT = MVT::i8;

18
test/CodeGen/X86/stack-align-memcpy.ll Normal file
View File

@ -0,0 +1,18 @@
; RUN: llc < %s -force-align-stack -mtriple i386-apple-darwin -mcpu=i486 | FileCheck %s
%struct.foo = type { [88 x i8] }
; PR15249
; We can't use rep;movsl here because it clobbers the base pointer in %esi.
define void @test1(%struct.foo* nocapture %x, i32 %y) nounwind {
%dynalloc = alloca i8, i32 %y, align 1
call void @bar(i8* %dynalloc, %struct.foo* align 4 byval %x)
ret void
; CHECK: test1:
; CHECK: andl $-16, %esp
; CHECK: movl %esp, %esi
; CHECK-NOT: rep;movsl
}
declare void @bar(i8* nocapture, %struct.foo* align 4 byval) nounwind