[PATCH] D139321: InstCombine: Fix metadata arguments blocking freeze combining

[Matt Arsenault via Phabricator via llvm-commits]

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These are used for special arguments to intrinsics and don't make any
sense to consider for poisonness. Fixes not pushing freeze through
llvm.fptrunc.round.

      

92106641ae297c24877085e0357e8095aa7b43c9 <https://reviews.llvm.org/rG92106641ae297c24877085e0357e8095aa7b43c9> made
isGuaranteedNotToBeUndefOrPoison return false for metadata arguments,
which doesn't entirely make sense. An alternate patch could switch
that to true, and try to filter out adding some pointless noundefs on
metadata arguments (I tried that, attributor breaks one case with a
llvm.dbg.value in it).


https://reviews.llvm.org/D139321

Files:
  llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
  llvm/test/Transforms/InstCombine/freeze-fp-ops.ll


Index: llvm/test/Transforms/InstCombine/freeze-fp-ops.ll
===================================================================
--- llvm/test/Transforms/InstCombine/freeze-fp-ops.ll
+++ llvm/test/Transforms/InstCombine/freeze-fp-ops.ll
@@ -508,9 +508,9 @@
 
 define float @freeze_fptrunc_round(double %arg0) {
 ; CHECK-LABEL: @freeze_fptrunc_round(
-; CHECK-NEXT:    [[OP:%.*]] = call float @llvm.fptrunc.round.f32.f64(double [[ARG0:%.*]], metadata !"round.downward")
-; CHECK-NEXT:    [[FREEZE:%.*]] = freeze float [[OP]]
-; CHECK-NEXT:    ret float [[FREEZE]]
+; CHECK-NEXT:    [[ARG0_FR:%.*]] = freeze double [[ARG0:%.*]]
+; CHECK-NEXT:    [[OP:%.*]] = call float @llvm.fptrunc.round.f32.f64(double [[ARG0_FR]], metadata !"round.downward")
+; CHECK-NEXT:    ret float [[OP]]
 ;
   %op = call float @llvm.fptrunc.round.f32.f64(double %arg0, metadata !"round.downward")
   %freeze = freeze float %op
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3803,7 +3803,8 @@
   // poison.
   Use *MaybePoisonOperand = nullptr;
   for (Use &U : OrigOpInst->operands()) {
-    if (isGuaranteedNotToBeUndefOrPoison(U.get()))
+    if (isa<MetadataAsValue>(U.get()) ||
+        isGuaranteedNotToBeUndefOrPoison(U.get()))
       continue;
     if (!MaybePoisonOperand)
       MaybePoisonOperand = &U;


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