When TCO is turned on, it is possible to end up with aliasing FrameIndex's. Therefore,

CombinerAA cannot assume that different FrameIndex's never alias, but can instead use
MachineFrameInfo to get the actual offsets of these slots and check for actual aliasing.

This fixes CodeGen/X86/2010-02-19-TailCallRetAddrBug.ll and CodeGen/X86/tailcallstack64.ll
when CombinerAA is enabled, modulo a different register allocation sequence.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114348 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c9c4d91e973610487a8149e843d45f2e5438c474..91e370b27195f3239a5fdd7b7b72c38eaadcb951 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7030,8 +7030,19 @@ bool DAGCombiner::isAlias(SDValue Ptr1, int64_t Size1,
   if (Base1 == Base2 || (GV1 && (GV1 == GV2)) || (CV1 && (CV1 == CV2)))
     return !((Offset1 + Size1) <= Offset2 || (Offset2 + Size2) <= Offset1);
 
-  // If we know what the bases are, and they aren't identical, then we know they
-  // cannot alias.
+  // It is possible for different frame indices to alias each other, mostly
+  // when tail call optimization reuses return address slots for arguments.
+  // To catch this case, look up the actual index of frame indices to compute
+  // the real alias relationship.
+  if (isFrameIndex1 && isFrameIndex2) {
+    MachineFrameInfo *MFI = DAG.getMachineFunction().getFrameInfo();
+    Offset1 += MFI->getObjectOffset(cast<FrameIndexSDNode>(Base1)->getIndex());
+    Offset2 += MFI->getObjectOffset(cast<FrameIndexSDNode>(Base2)->getIndex());
+    return !((Offset1 + Size1) <= Offset2 || (Offset2 + Size2) <= Offset1);
+  }
+
+  // Otherwise, if we know what the bases are, and they aren't identical, then 
+  // we know they cannot alias.
   if ((isFrameIndex1 || CV1 || GV1) && (isFrameIndex2 || CV2 || GV2))
     return false;
 

diff --git a/test/CodeGen/X86/2010-09-17-SideEffectsInChain.ll b/test/CodeGen/X86/2010-09-17-SideEffectsInChain.ll
index 35434ffafaf765a97393b83d56b8d0d30ddb95e2..8fe0309421e509e03a60979f639a982592c441b9 100644 (file)
--- a/test/CodeGen/X86/2010-09-17-SideEffectsInChain.ll
+++ b/test/CodeGen/X86/2010-09-17-SideEffectsInChain.ll
@@ -19,8 +19,8 @@ entry:
 }
 
 ; CHECK: movq  ___stack_chk_guard@GOTPCREL(%rip), %rax
-; CHECK: movb  (%rsp), %dl
-; CHECK-NEXT: movb     30(%rsp), %sil
-; CHECK: movb  %dl, (%rsp)
-; CHECK-NEXT: movb     %sil, 30(%rsp)
+; CHECK: movb  30(%rsp), %dl
+; CHECK: movb  (%rsp), %sil
+; CHECK: movb  %sil, (%rsp)
+; CHECK: movb  %dl, 30(%rsp)
 ; CHECK: callq ___stack_chk_fail