From 01403f97110aa3fe45f1188ffb0fd07b6aa28207 Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Mon, 14 Mar 2016 20:18:59 +0000 Subject: [PATCH] allow branch weight metadata on select instructions (PR26636) As noted in: https://llvm.org/bugs/show_bug.cgi?id=26636 This doesn't accomplish anything on its own. It's the first step towards preserving and using branch weights with selects. The next step would be to make sure we're propagating the info in all of the other places where we create selects (SimplifyCFG, InstCombine, etc). I don't think there's an easy fix to make this happen; we have to look at each transform individually to determine how to correctly propagate the weights. Along with that step, we need to then use the weights when making subsequent transform decisions such as discussed in http://reviews.llvm.org/D16836. The inliner test is independent but closely related. It verifies that metadata is preserved when both branches and selects are cloned. Differential Revision: http://reviews.llvm.org/D18133 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@263482 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/llvm/IR/IRBuilder.h | 8 +++- lib/Transforms/Utils/SimplifyCFG.cpp | 3 +- test/Transforms/Inline/profile-meta.ll | 41 ++++++++++++++++++++ test/Transforms/SimplifyCFG/PhiEliminate2.ll | 11 +++++- 4 files changed, 58 insertions(+), 5 deletions(-) create mode 100644 test/Transforms/Inline/profile-meta.ll diff --git a/include/llvm/IR/IRBuilder.h b/include/llvm/IR/IRBuilder.h index c6c12fa2225..a9c9c81719f 100644 --- a/include/llvm/IR/IRBuilder.h +++ b/include/llvm/IR/IRBuilder.h @@ -1569,12 +1569,16 @@ public: } Value *CreateSelect(Value *C, Value *True, Value *False, - const Twine &Name = "") { + const Twine &Name = "", MDNode *ProfWeights = nullptr) { if (Constant *CC = dyn_cast(C)) if (Constant *TC = dyn_cast(True)) if (Constant *FC = dyn_cast(False)) return Insert(Folder.CreateSelect(CC, TC, FC), Name); - return Insert(SelectInst::Create(C, True, False), Name); + + SelectInst *Sel = SelectInst::Create(C, True, False); + // TODO: "unpredictable" metadata can apply to a select too. + Sel->setMetadata(LLVMContext::MD_prof, ProfWeights); + return Insert(Sel, Name); } VAArgInst *CreateVAArg(Value *List, Type *Ty, const Twine &Name = "") { diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp index b08fb043f1a..bf94e2629ca 100644 --- a/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/lib/Transforms/Utils/SimplifyCFG.cpp @@ -1935,7 +1935,8 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI, Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); - Value *Select = Builder.CreateSelect(IfCond, TrueVal, FalseVal); + MDNode *MDN = InsertPt->getMetadata(LLVMContext::MD_prof); + Value *Select = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", MDN); PN->replaceAllUsesWith(Select); Select->takeName(PN); PN->eraseFromParent(); diff --git a/test/Transforms/Inline/profile-meta.ll b/test/Transforms/Inline/profile-meta.ll new file mode 100644 index 00000000000..5000b83f2f3 --- /dev/null +++ b/test/Transforms/Inline/profile-meta.ll @@ -0,0 +1,41 @@ +; RUN: opt < %s -S -inline | FileCheck %s + +; Make sure that profile metadata is preserved when cloning a select. + +define i32 @callee_with_select(i1 %c, i32 %a, i32 %b) { + %sel = select i1 %c, i32 %a, i32 %b, !prof !0 + ret i32 %sel +} + +define i32 @caller_of_select(i1 %C, i32 %A, i32 %B) { + %ret = call i32 @callee_with_select(i1 %C, i32 %A, i32 %B) + ret i32 %ret + +; CHECK-LABEL: @caller_of_select( +; CHECK-NEXT: [[SEL:%.*]] = select i1 %C, i32 %A, i32 %B, !prof !0 +; CHECK-NEXT: ret i32 [[SEL]] +} + +; Make sure that profile metadata is preserved when cloning a branch. + +define i32 @callee_with_branch(i1 %c) { + br i1 %c, label %if, label %else, !prof !1 +if: + ret i32 1 +else: + ret i32 2 +} + +define i32 @caller_of_branch(i1 %C) { + %ret = call i32 @callee_with_branch(i1 %C) + ret i32 %ret + +; CHECK-LABEL: @caller_of_branch( +; CHECK-NEXT: br i1 %C, label %{{.*}}, label %{{.*}}, !prof !1 +} + +!0 = !{!"branch_weights", i32 1, i32 2} +!1 = !{!"branch_weights", i32 3, i32 4} +; CHECK: !0 = !{!"branch_weights", i32 1, i32 2} +; CHECK: !1 = !{!"branch_weights", i32 3, i32 4} + diff --git a/test/Transforms/SimplifyCFG/PhiEliminate2.ll b/test/Transforms/SimplifyCFG/PhiEliminate2.ll index fcda12c5279..60931fc71aa 100644 --- a/test/Transforms/SimplifyCFG/PhiEliminate2.ll +++ b/test/Transforms/SimplifyCFG/PhiEliminate2.ll @@ -1,8 +1,11 @@ ; RUN: opt < %s -simplifycfg -S | FileCheck %s +; Use a select to make this a single BB. +; Also, make sure the profile metadata is propagated to the select (PR26636). + define i32 @FoldTwoEntryPHINode(i1 %C, i32 %V1, i32 %V2, i16 %V3) { entry: - br i1 %C, label %then, label %else + br i1 %C, label %then, label %else, !prof !0 then: %V4 = or i32 %V2, %V1 br label %Cont @@ -18,8 +21,12 @@ Cont: ; CHECK-NEXT: entry: ; CHECK-NEXT: %V5 = sext i16 %V3 to i32 ; CHECK-NEXT: %V4 = or i32 %V2, %V1 -; CHECK-NEXT: %V6 = select i1 %C, i32 %V4, i32 %V5 +; CHECK-NEXT: %V6 = select i1 %C, i32 %V4, i32 %V5, !prof !0 ; CHECK-NEXT: %0 = call i32 @FoldTwoEntryPHINode(i1 false, i32 0, i32 0, i16 0) ; CHECK-NEXT: ret i32 %V1 } +!0 = !{!"branch_weights", i32 3, i32 5} + +; CHECK: !0 = !{!"branch_weights", i32 3, i32 5} +