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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70179 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index b937eaff757cd2a271c980f614aa04c576d84325..bd4b10ea4e4230a6082ddf2df945f04cf7063ed1 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/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/test/CodeGen/X86/fold-sext-trunc.ll b/test/CodeGen/X86/fold-sext-trunc.ll
new file mode 100644 (file)
index 0000000..1016b10
--- /dev/null
+++ b/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
+}