[InstCombine] Treat identical operands as one in pushFreezeToPreventPoisonFromPropagating

To push a freeze through an instruction, only one operand may produce
poison. However, this currently fails for identical operands which are
treated as separate. This patch fixes this by treating them as a single
operand.

Author: c-rhodes

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -4902,7 +4902,9 @@ InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating(FreezeInst &OrigFI) {
   Use *MaybePoisonOperand = nullptr;
   for (Use &U : OrigOpInst->operands()) {
     if (isa<MetadataAsValue>(U.get()) ||
-        isGuaranteedNotToBeUndefOrPoison(U.get()))
+        isGuaranteedNotToBeUndefOrPoison(U.get()) ||
+        // Treat identical operands as a single operand.
+        (MaybePoisonOperand && MaybePoisonOperand->get() == U.get()))
       continue;
     if (!MaybePoisonOperand)
       MaybePoisonOperand = &U;

llvm/test/Transforms/InstCombine/freeze.ll

@@ -144,9 +144,9 @@ define i32 @early_freeze_test3(i32 %v1) {
 
 define i32 @early_freeze_test4(i32 %v1) {
 ; CHECK-LABEL: @early_freeze_test4(
-; CHECK-NEXT:    [[V2:%.*]] = mul i32 [[V1_FR:%.*]], [[V1_FR]]
-; CHECK-NEXT:    [[V2_FR:%.*]] = freeze i32 [[V2]]
-; CHECK-NEXT:    ret i32 [[V2_FR]]
+; CHECK-NEXT:    [[V2_FR:%.*]] = freeze i32 [[V2:%.*]]
+; CHECK-NEXT:    [[V3:%.*]] = mul i32 [[V2_FR]], [[V2_FR]]
+; CHECK-NEXT:    ret i32 [[V3]]
 ;
   %v2 = mul i32 %v1, %v1
   %v2.fr = freeze i32 %v2