[PATCH] D84818: [JumpThreading] Fold br(freeze(undef))
Juneyoung Lee via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Jul 28 18:47:29 PDT 2020
aqjune created this revision.
aqjune added reviewers: efriedma, nikic, kazu.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.
aqjune requested review of this revision.
This patch makes JumpThreading fold br(freeze(undef)) if the freeze instruction
is only used by the branch.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D84818
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
@@ -128,19 +128,13 @@
define i32 @test1_undef(i1 %cond) {
; CHECK-LABEL: @test1_undef(
-; 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: [[A_FR:%.*]] = freeze i1 undef
-; CHECK-NEXT: br i1 [[A_FR]], label [[T2]], label [[F2:%.*]]
+; CHECK-NEXT: br i1 [[COND:%.*]], label [[T2:%.*]], label [[F2:%.*]]
; CHECK: T2:
-; CHECK-NEXT: [[B4:%.*]] = phi i32 [ [[V1]], [[MERGE_THREAD]] ], [ [[V2]], [[MERGE]] ]
+; CHECK-NEXT: [[V1:%.*]] = call i32 @f1()
; CHECK-NEXT: call void @f3()
-; CHECK-NEXT: ret i32 [[B4]]
+; CHECK-NEXT: ret i32 [[V1]]
; CHECK: F2:
+; CHECK-NEXT: [[V2:%.*]] = call i32 @f2()
; 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
@@ -1057,9 +1057,11 @@
}
}
- // If the terminator is branching on an undef, we can pick any of the
- // successors to branch to. Let GetBestDestForJumpOnUndef decide.
- if (isa<UndefValue>(Condition)) {
+ // If the terminator is branching on an undef or freeze undef, we can pick any
+ // of the successors to branch to. Let GetBestDestForJumpOnUndef decide.
+ auto *FI = dyn_cast<FreezeInst>(Condition);
+ if (isa<UndefValue>(Condition) ||
+ (FI && isa<UndefValue>(FI->getOperand(0)) && FI->hasOneUse())) {
unsigned BestSucc = GetBestDestForJumpOnUndef(BB);
std::vector<DominatorTree::UpdateType> Updates;
@@ -1078,6 +1080,8 @@
BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm);
BBTerm->eraseFromParent();
DTU->applyUpdatesPermissive(Updates);
+ if (FI)
+ FI->eraseFromParent();
return true;
}
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