[llvm] r175057 - X86: Disable generation of rep; movsl when %esi is used as a base pointer.

[Benjamin Kramer]

Author: d0k
Date: Wed Feb 13 07:40:35 2013
New Revision: 175057

URL: http://llvm.org/viewvc/llvm-project?rev=175057&view=rev
Log:
X86: Disable generation of rep;movsl when %esi is used as a base pointer.

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.

Added:
    llvm/trunk/test/CodeGen/X86/stack-align-memcpy.ll
Modified:
    llvm/trunk/lib/Target/X86/X86SelectionDAGInfo.cpp

Modified: llvm/trunk/lib/Target/X86/X86SelectionDAGInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86SelectionDAGInfo.cpp?rev=175057&r1=175056&r2=175057&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86SelectionDAGInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86SelectionDAGInfo.cpp Wed Feb 13 07:40:35 2013
@@ -202,6 +202,14 @@ X86SelectionDAGInfo::EmitTargetCodeForMe
       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;

Added: llvm/trunk/test/CodeGen/X86/stack-align-memcpy.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/stack-align-memcpy.ll?rev=175057&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/stack-align-memcpy.ll (added)
+++ llvm/trunk/test/CodeGen/X86/stack-align-memcpy.ll Wed Feb 13 07:40:35 2013
@@ -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