Author: alex-t Date: 2020-12-17T02:40:54+03:00 New Revision: 35ec3ff76dee376661dd7e4971b80533a7a7f364
URL: https://github.com/llvm/llvm-project/commit/35ec3ff76dee376661dd7e4971b80533a7a7f364 DIFF: https://github.com/llvm/llvm-project/commit/35ec3ff76dee376661dd7e4971b80533a7a7f364.diff LOG: Disable Jump Threading for the targets with divergent control flow Details: Jump Threading does not make sense for the targets with divergent CF since they do not use branch prediction for speculative execution. Also in the high level IR there is no enough information to conclude that the branch is divergent or uniform. This may cause errors in further CF lowering. Reviewed By: rampitec Differential Revision: https://reviews.llvm.org/D93302 Added: llvm/test/Transforms/JumpThreading/divergent-target-test.ll Modified: llvm/lib/Transforms/Scalar/JumpThreading.cpp Removed: ################################################################################ diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp index a24dd8029f68..ce191144297b 100644 --- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp +++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp @@ -32,6 +32,7 @@ #include "llvm/Analysis/Loads.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Analysis/TargetTransformInfo.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/IR/BasicBlock.h" #include "llvm/IR/CFG.h" @@ -153,6 +154,7 @@ namespace { AU.addPreserved<LazyValueInfoWrapperPass>(); AU.addPreserved<GlobalsAAWrapperPass>(); AU.addRequired<TargetLibraryInfoWrapperPass>(); + AU.addRequired<TargetTransformInfoWrapperPass>(); } void releaseMemory() override { Impl.releaseMemory(); } @@ -311,6 +313,10 @@ static void updatePredecessorProfileMetadata(PHINode *PN, BasicBlock *BB) { bool JumpThreading::runOnFunction(Function &F) { if (skipFunction(F)) return false; + auto TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); + // Jump Threading has no sense for the targets with divergent CF + if (TTI->hasBranchDivergence()) + return false; auto TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); auto DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); auto LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI(); diff --git a/llvm/test/Transforms/JumpThreading/divergent-target-test.ll b/llvm/test/Transforms/JumpThreading/divergent-target-test.ll new file mode 100644 index 000000000000..4f7d237691c8 --- /dev/null +++ b/llvm/test/Transforms/JumpThreading/divergent-target-test.ll @@ -0,0 +1,47 @@ +; REQUIRES: amdgpu-registered-target && x86-registered-target +; RUN: opt < %s -mtriple=amdgcn -jump-threading -S | FileCheck %s -check-prefixes=CHECK,DIVERGENT +; RUN: opt < %s -mtriple=x86_64 -jump-threading -S | FileCheck %s -check-prefixes=CHECK,UNIFORM + +; Here we assure that for the target with no branch divergence usual Jump Threading optimization performed +; For target with branch divergence - no optimization, so the IR is unchanged. + +declare i32 @f1() +declare i32 @f2() +declare void @f3() + +define i32 @test(i1 %cond) { +; CHECK: test + br i1 %cond, label %T1, label %F1 + +; DIVERGENT: T1 +; UNIFORM-NOT: T1 +T1: + %v1 = call i32 @f1() + br label %Merge +; DIVERGENT: F1 +; UNIFORM-NOT: F1 +F1: + %v2 = call i32 @f2() + br label %Merge +; DIVERGENT: Merge +; UNIFORM-NOT: Merge +Merge: + %A = phi i1 [true, %T1], [false, %F1] + %B = phi i32 [%v1, %T1], [%v2, %F1] + br i1 %A, label %T2, label %F2 + +; DIVERGENT: T2 +T2: +; UNIFORM: T2: +; UNIFORM: %v1 = call i32 @f1() +; UNIFORM: call void @f3() +; UNIFORM: ret i32 %v1 + call void @f3() + ret i32 %B +; DIVERGENT: F2 +F2: +; UNIFORM: F2: +; UNIFORM: %v2 = call i32 @f2() +; UNIFORM: ret i32 %v2 + ret i32 %B +} _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
