fix PR10605 / rdar://9930964 by adding a pretty scary missed check.

It's somewhat surprising anything works without this.  Before we would
compile the testcase into:

test:                                   # @test
	movl	$4, 8(%rdi)
	movl	8(%rdi), %eax
	orl	%esi, %eax
	cmpl	$32, %edx
	movl	%eax, -4(%rsp)          # 4-byte Spill
	je	.LBB0_2

now we produce:

test:                                   # @test
	movl	8(%rdi), %eax
	movl	$4, 8(%rdi)
	orl	%esi, %eax
	cmpl	$32, %edx
	movl	%eax, -4(%rsp)          # 4-byte Spill
	je	.LBB0_2
llvm-svn: 137303

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 87bb296b8c7..ec8f014f651 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -754,6 +754,11 @@ bool SelectionDAGISel::TryToFoldFastISelLoad(const LoadInst *LI,
     TheUser = TheUser->use_back();
   }
   
+  // If we didn't find the fold instruction, then we failed to collapse the
+  // sequence.
+  if (TheUser != FoldInst)
+    return false;
+  
   // Don't try to fold volatile loads.  Target has to deal with alignment
   // constraints.
   if (LI->isVolatile()) return false;