When transforming sext(trunc(load(x))) into sext(smaller load(x)),

the trunc is directly replaced with the smaller load, so don't
try to create a new sext node. This fixes PR4050.

llvm-svn: 70179

2 files changed, 21 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index b937eaff757..bd4b10ea4e4 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2962,7 +2962,7 @@ SDValue DAGCombiner::visitSIGN_EXTEND(SDNode *N) {
     if (NarrowLoad.getNode()) {
       if (NarrowLoad.getNode() != N0.getNode())
         CombineTo(N0.getNode(), NarrowLoad);
-      return DAG.getNode(ISD::SIGN_EXTEND, N->getDebugLoc(), VT, NarrowLoad);
+      return SDValue(N, 0);   // Return N so it doesn't get rechecked!
     }
 
     // See if the value being truncated is already sign extended.  If so, just
diff --git a/llvm/test/CodeGen/X86/fold-sext-trunc.ll b/llvm/test/CodeGen/X86/fold-sext-trunc.ll
new file mode 100644
index 00000000000..1016b1081aa
--- /dev/null
+++ b/llvm/test/CodeGen/X86/fold-sext-trunc.ll
@@ -0,0 +1,20 @@
+; RUN: llvm-as < %s | llc -march=x86-64 | grep movslq | count 1
+; PR4050
+
+	type { i64 }		; type %0
+	%struct.S1 = type { i16, i32 }
+@g_10 = external global %struct.S1		; <%struct.S1*> [#uses=2]
+
+declare void @func_28(i64, i64)
+
+define void @int322(i32 %foo) nounwind {
+entry:
+	%val = load i64* getelementptr (%0* bitcast (%struct.S1* @g_10 to %0*), i32 0, i32 0)		; <i64> [#uses=1]
+	%0 = load i32* getelementptr (%struct.S1* @g_10, i32 0, i32 1), align 4		; <i32> [#uses=1]
+	%1 = sext i32 %0 to i64		; <i64> [#uses=1]
+	%tmp4.i = lshr i64 %val, 32		; <i64> [#uses=1]
+	%tmp5.i = trunc i64 %tmp4.i to i32		; <i32> [#uses=1]
+	%2 = sext i32 %tmp5.i to i64		; <i64> [#uses=1]
+	tail call void @func_28(i64 %2, i64 %1) nounwind
+	ret void
+}