Check for dynamic allocas and inline asm that clobbers sp before building

selection dag (PR19012)

In X86SelectionDagInfo::EmitTargetCodeForMemcpy we check with MachineFrameInfo
to make sure that ESI isn't used as a base pointer register before we choose to
emit rep movs (which clobbers esi).

The problem is that MachineFrameInfo wouldn't know about dynamic allocas or
inline asm that clobbers the stack pointer until SelectionDAGBuilder has
encountered them.

This patch fixes the problem by checking for such things when building the
FunctionLoweringInfo.

Differential Revision: http://llvm-reviews.chandlerc.com/D2954

llvm-svn: 202930

1 files changed, 26 insertions, 1 deletions

diff --git a/llvm/test/CodeGen/X86/stack-align-memcpy.ll b/llvm/test/CodeGen/X86/stack-align-memcpy.ll
index 87bb85fad83..0cc3aa84889 100644
--- a/llvm/test/CodeGen/X86/stack-align-memcpy.ll
+++ b/llvm/test/CodeGen/X86/stack-align-memcpy.ll
@@ -2,6 +2,9 @@
 
 %struct.foo = type { [88 x i8] }
 
+declare void @bar(i8* nocapture, %struct.foo* align 4 byval) nounwind
+declare void @baz(i8*) nounwind
+
 ; 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 {
@@ -15,4 +18,26 @@ define void @test1(%struct.foo* nocapture %x, i32 %y) nounwind {
 ; CHECK-NOT: rep;movsl
 }
 
-declare void @bar(i8* nocapture, %struct.foo* align 4 byval) nounwind
+; PR19012
+; Also don't clobber %esi if the dynamic alloca comes after the memcpy.
+define void @test2(%struct.foo* nocapture %x, i32 %y, i8* %z) nounwind {
+  call void @bar(i8* %z, %struct.foo* align 4 byval %x)
+  %dynalloc = alloca i8, i32 %y, align 1
+  call void @baz(i8* %dynalloc)
+  ret void
+
+; CHECK-LABEL: test2:
+; CHECK: movl %esp, %esi
+; CHECK-NOT: rep;movsl
+}
+
+; Check that we do use rep movs if we make the alloca static.
+define void @test3(%struct.foo* nocapture %x, i32 %y, i8* %z) nounwind {
+  call void @bar(i8* %z, %struct.foo* align 4 byval %x)
+  %statalloc = alloca i8, i32 8, align 1
+  call void @baz(i8* %statalloc)
+  ret void
+
+; CHECK-LABEL: test3:
+; CHECK: rep;movsl
+}