[InstCombine] Avoid ConstantExpr::get() call

Avoid calling ConstantExpr::get() for associative/commutative
binops, call ConstantFoldBinaryOpOperands() instead. We only
want to perform the reassociation of the constants actually fold.

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 0335815..6c27296 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -523,11 +523,12 @@ bool InstCombinerImpl::SimplifyAssociativeOrCommutative(BinaryOperator &I) {
       // Transform: "(A op C1) op (B op C2)" ==> "(A op B) op (C1 op C2)"
       // if C1 and C2 are constants.
       Value *A, *B;
-      Constant *C1, *C2;
+      Constant *C1, *C2, *CRes;
       if (Op0 && Op1 &&
           Op0->getOpcode() == Opcode && Op1->getOpcode() == Opcode &&
           match(Op0, m_OneUse(m_BinOp(m_Value(A), m_Constant(C1)))) &&
-          match(Op1, m_OneUse(m_BinOp(m_Value(B), m_Constant(C2))))) {
+          match(Op1, m_OneUse(m_BinOp(m_Value(B), m_Constant(C2)))) &&
+          (CRes = ConstantFoldBinaryOpOperands(Opcode, C1, C2, DL))) {
         bool IsNUW = hasNoUnsignedWrap(I) &&
            hasNoUnsignedWrap(*Op0) &&
            hasNoUnsignedWrap(*Op1);
@@ -544,7 +545,7 @@ bool InstCombinerImpl::SimplifyAssociativeOrCommutative(BinaryOperator &I) {
         InsertNewInstWith(NewBO, I);
         NewBO->takeName(Op1);
         replaceOperand(I, 0, NewBO);
-        replaceOperand(I, 1, ConstantExpr::get(Opcode, C1, C2));
+        replaceOperand(I, 1, CRes);
         // Conservatively clear the optional flags, since they may not be
         // preserved by the reassociation.
         ClearSubclassDataAfterReassociation(I);