[PATCH] D84949: [JumpThreading] Don't limit the type of an operand

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune created this revision.
aqjune added reviewers: efriedma, nikic, lebedev.ri.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.
aqjune requested review of this revision.

Compared to the optimized code with branch conditions never frozen,
limiting the type of freeze's operand causes generation of suboptimal code in
some cases.
I would like to suggest removing the constraint, as this patch does.
If the number of freeze instructions becomes significant, this can be revisited.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D84949

Files:
  llvm/lib/Transforms/Scalar/JumpThreading.cpp
  llvm/test/Transforms/JumpThreading/freeze.ll


Index: llvm/test/Transforms/JumpThreading/freeze.ll
===================================================================
--- llvm/test/Transforms/JumpThreading/freeze.ll
+++ llvm/test/Transforms/JumpThreading/freeze.ll
@@ -85,20 +85,14 @@
 
 define i32 @test1_cast2(i1 %cond) {
 ; CHECK-LABEL: @test1_cast2(
-; CHECK-NEXT:    br i1 [[COND:%.*]], label [[MERGE_THREAD:%.*]], label [[MERGE:%.*]]
-; CHECK:       Merge.thread:
-; CHECK-NEXT:    [[V1:%.*]] = call i32 @f1()
-; CHECK-NEXT:    br label [[T2:%.*]]
-; CHECK:       Merge:
-; CHECK-NEXT:    [[V2:%.*]] = call i32 @f2()
-; CHECK-NEXT:    [[A0_FR:%.*]] = freeze i32 0
-; CHECK-NEXT:    [[A_FR:%.*]] = trunc i32 [[A0_FR]] to i1
-; CHECK-NEXT:    br i1 [[A_FR]], label [[T2]], label [[F2:%.*]]
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[T2:%.*]], label [[F2:%.*]]
 ; CHECK:       T2:
-; CHECK-NEXT:    [[B5:%.*]] = phi i32 [ [[V1]], [[MERGE_THREAD]] ], [ [[V2]], [[MERGE]] ]
+; CHECK-NEXT:    [[V1:%.*]] = call i32 @f1()
 ; CHECK-NEXT:    call void @f3()
-; CHECK-NEXT:    ret i32 [[B5]]
+; CHECK-NEXT:    ret i32 [[V1]]
 ; CHECK:       F2:
+; CHECK-NEXT:    [[V2:%.*]] = call i32 @f2()
+; CHECK-NEXT:    [[A0_FR:%.*]] = freeze i32 0
 ; CHECK-NEXT:    ret i32 [[V2]]
 ;
   br i1 %cond, label %T1, label %F1
Index: llvm/lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -700,12 +700,10 @@
     return true;
   }
 
-  // Handle Freeze instructions, in a manner similar to Cast.
   if (FreezeInst *FI = dyn_cast<FreezeInst>(I)) {
     Value *Source = FI->getOperand(0);
-    if (!isa<PHINode>(Source) && !isa<CmpInst>(Source) &&
-        !isa<CastInst>(Source))
-      return false;
+    // Unlike cast, don't limit the type of Source because it generates a
+    // sub-optimal code compared to the case when branch conditions are unfrozen
     ComputeValueKnownInPredecessorsImpl(Source, BB, Result, Preference,
                                         RecursionSet, CxtI);
 


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