Don't fold negative constants into addresss displacements for memory references

This results in trying to reference a negative offset from r15.

R=sehr@chromium.org,jvoung@chromium.org,eliben@chromium.org
BUG= https://code.google.com/p/nativeclient/issues/detail?id=3302

Review URL: https://codereview.chromium.org/12277018

2 files changed, 22 insertions, 0 deletions

diff --git a/lib/Target/X86/X86ISelDAGToDAG.cpp b/lib/Target/X86/X86ISelDAGToDAG.cpp
index 70cfa7d516..f4a9ca38d2 100644
--- a/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -607,6 +607,14 @@ bool X86DAGToDAGISel::FoldOffsetIntoAddress(uint64_t Offset,
     if (AM.BaseType == X86ISelAddressMode::FrameIndexBase &&
         !isDispSafeForFrameIndex(Val))
       return true;
+    // LOCALMOD-BEGIN
+    // Do not allow negative displacements to be folded into memory operations.
+    // This results in trying to dereference a negative offset from RZP
+    else if (Subtarget->isTargetNaCl64() &&
+             AM.BaseType == X86ISelAddressMode::RegBase && Val < 0 &&
+             selectingMemOp)
+      return true;
+    // LOCALMOD-END
   }
   AM.Disp = Val;
   return false;
diff --git a/test/NaCl/X86/nacl64-addrmodes.ll b/test/NaCl/X86/nacl64-addrmodes.ll
new file mode 100644
index 0000000000..772424b154
--- /dev/null
+++ b/test/NaCl/X86/nacl64-addrmodes.ll
@@ -0,0 +1,14 @@
+; RUN: llc -mtriple=x86_64-unknown-nacl -filetype=asm %s -o - \
+; RUN:   | FileCheck %s
+
+; Check that we don't try to fold a negative displacement into a memory
+; reference
+define i16 @negativedisp(i32 %b) {
+; CHECK: negativedisp
+  %a = alloca [1 x i16], align 2
+  %add = add nsw i32 1073741824, %b
+  %arrayidx = getelementptr inbounds [1 x i16]* %a, i32 0, i32 %add
+; CHECK-NOT: nacl:-2147483648(
+  %c = load i16* %arrayidx, align 2
+  ret i16 %c
+}