InstCombine: Don't create an unused instruction

We would create an instruction but not inserting it. Not inserting the unused instruction would lead us to verification failure. This fixes PR21653. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222659 91177308-0d34-0410-b5e6-96231b3b80d8
bgamari · Nov 24, 2014 · a17a9dc · a17a9dc
1 parent c195267
commit a17a9dc
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Showing 2 changed files with 11 additions and 2 deletions.
diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -300,8 +300,7 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
     if (match(Op0, m_Shl(m_One(), m_Value(Y)))) {
       BO = BinaryOperator::CreateShl(Op1, Y);
       ShlNSW = cast<BinaryOperator>(Op0)->hasNoSignedWrap();
-    }
-    if (match(Op1, m_Shl(m_One(), m_Value(Y)))) {
+    } else if (match(Op1, m_Shl(m_One(), m_Value(Y)))) {
       BO = BinaryOperator::CreateShl(Op0, Y);
       ShlNSW = cast<BinaryOperator>(Op1)->hasNoSignedWrap();
     }

diff --git a/test/Transforms/InstCombine/mul.ll b/test/Transforms/InstCombine/mul.ll
@@ -245,3 +245,13 @@ define i32 @test27(i32 %A, i32 %B) {
         ret i32 %D
 ; CHECK: shl nuw i32 %A, %B
 }
+
+define i32 @test28(i32 %A) {
+; CHECK-LABEL: @test28(
+        %B = shl i32 1, %A
+        %C = mul nsw i32 %B, %B
+        ret i32 %C
+; CHECK:      %[[shl1:.*]] = shl i32 1, %A
+; CHECK-NEXT: %[[shl2:.*]] = shl i32 %[[shl1]], %A
+; CHECK-NEXT: ret i32 %[[shl2]]
+}