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[SLU][profcheck] create likely branch weights for guard->branch #164271

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Merged
merged 1 commit into from
Nov 5, 2025
+25 −13
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[SLU][profcheck] create likely branch weights for guard->branch #164271

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12 changes: 9 additions & 3 deletions llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/ProfDataUtils.h"
Expand Down Expand Up @@ -2831,9 +2832,14 @@ static BranchInst *turnGuardIntoBranch(IntrinsicInst *GI, Loop &L,
MSSAU->getMemorySSA()->verifyMemorySSA();

DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
Instruction *DeoptBlockTerm =
SplitBlockAndInsertIfThen(GI->getArgOperand(0), GI, true,
GI->getMetadata(LLVMContext::MD_prof), &DTU, &LI);
// llvm.experimental.guard doesn't have branch weights. We can assume,
// however, that the deopt path is unlikely.
Instruction *DeoptBlockTerm = SplitBlockAndInsertIfThen(
GI->getArgOperand(0), GI, true,
!ProfcheckDisableMetadataFixes && EstimateProfile
? MDBuilder(GI->getContext()).createUnlikelyBranchWeights()
: nullptr,
&DTU, &LI);
BranchInst *CheckBI = cast<BranchInst>(CheckBB->getTerminator());
// SplitBlockAndInsertIfThen inserts control flow that branches to
// DeoptBlockTerm if the condition is true. We want the opposite.
Expand Down
26 changes: 16 additions & 10 deletions llvm/test/Transforms/SimpleLoopUnswitch/guards.ll
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Original file line number Diff line number Diff line change
@@ -1,15 +1,15 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --version 5
; RUN: opt -passes='loop(simple-loop-unswitch<nontrivial>),verify<loops>' -simple-loop-unswitch-guards -S < %s | FileCheck %s
; RUN: opt -passes='simple-loop-unswitch<nontrivial>' -simple-loop-unswitch-guards -S < %s | FileCheck %s
; RUN: opt -passes='loop-mssa(simple-loop-unswitch<nontrivial>),verify<loops>' -simple-loop-unswitch-guards -verify-memoryssa -verify-loop-info -S < %s | FileCheck %s

declare void @llvm.experimental.guard(i1, ...)

define void @test_simple_case(i1 %cond, i32 %N) {
define void @test_simple_case(i1 %cond, i32 %N) !prof !0 {
; CHECK-LABEL: define void @test_simple_case(
; CHECK-SAME: i1 [[COND:%.*]], i32 [[N:%.*]]) {
; CHECK-SAME: i1 [[COND:%.*]], i32 [[N:%.*]]) !prof [[PROF0:![0-9]+]] {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: br i1 [[COND]], label %[[ENTRY_SPLIT_US:.*]], label %[[ENTRY_SPLIT:.*]]
; CHECK-NEXT: br i1 [[COND]], label %[[ENTRY_SPLIT_US:.*]], label %[[ENTRY_SPLIT:.*]], !prof [[PROF1:![0-9]+]]
; CHECK: [[ENTRY_SPLIT_US]]:
; CHECK-NEXT: br label %[[LOOP_US:.*]]
; CHECK: [[LOOP_US]]:
Expand Down Expand Up @@ -50,9 +50,9 @@ define void @test_two_guards(i1 %cond1, i1 %cond2, i32 %N) {
; CHECK-LABEL: define void @test_two_guards(
; CHECK-SAME: i1 [[COND1:%.*]], i1 [[COND2:%.*]], i32 [[N:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: br i1 [[COND1]], label %[[ENTRY_SPLIT_US:.*]], label %[[ENTRY_SPLIT:.*]]
; CHECK-NEXT: br i1 [[COND1]], label %[[ENTRY_SPLIT_US:.*]], label %[[ENTRY_SPLIT:.*]], !prof [[PROF1]]
; CHECK: [[ENTRY_SPLIT_US]]:
; CHECK-NEXT: br i1 [[COND2]], label %[[ENTRY_SPLIT_US_SPLIT_US:.*]], label %[[ENTRY_SPLIT_US_SPLIT:.*]]
; CHECK-NEXT: br i1 [[COND2]], label %[[ENTRY_SPLIT_US_SPLIT_US:.*]], label %[[ENTRY_SPLIT_US_SPLIT:.*]], !prof [[PROF1]]
; CHECK: [[ENTRY_SPLIT_US_SPLIT_US]]:
; CHECK-NEXT: br label %[[LOOP_US_US:.*]]
; CHECK: [[LOOP_US_US]]:
Expand Down Expand Up @@ -108,7 +108,7 @@ define void @test_conditional_guards(i1 %cond, i32 %N) {
; CHECK-SAME: i1 [[COND:%.*]], i32 [[N:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[COND_FR:%.*]] = freeze i1 [[COND]]
; CHECK-NEXT: br i1 [[COND_FR]], label %[[ENTRY_SPLIT_US:.*]], label %[[ENTRY_SPLIT:.*]]
; CHECK-NEXT: br i1 [[COND_FR]], label %[[ENTRY_SPLIT_US:.*]], label %[[ENTRY_SPLIT:.*]], !prof [[PROF1]]
; CHECK: [[ENTRY_SPLIT_US]]:
; CHECK-NEXT: br label %[[LOOP_US:.*]]
; CHECK: [[LOOP_US]]:
Expand Down Expand Up @@ -171,7 +171,7 @@ define void @test_nested_loop(i1 %cond, i32 %N, i1 %arg) {
; CHECK-LABEL: define void @test_nested_loop(
; CHECK-SAME: i1 [[COND:%.*]], i32 [[N:%.*]], i1 [[ARG:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: br i1 [[COND]], label %[[ENTRY_SPLIT:.*]], label %[[OUTER_LOOP_SPLIT:.*]]
; CHECK-NEXT: br i1 [[COND]], label %[[ENTRY_SPLIT:.*]], label %[[OUTER_LOOP_SPLIT:.*]], !prof [[PROF1]]
; CHECK: [[ENTRY_SPLIT]]:
; CHECK-NEXT: br i1 [[ARG]], label %[[ENTRY_SPLIT_SPLIT_US:.*]], label %[[ENTRY_SPLIT_SPLIT:.*]]
; CHECK: [[ENTRY_SPLIT_SPLIT_US]]:
Expand Down Expand Up @@ -243,7 +243,7 @@ define void @test_sibling_loops(i1 %cond1, i1 %cond2, i32 %N) {
; CHECK-LABEL: define void @test_sibling_loops(
; CHECK-SAME: i1 [[COND1:%.*]], i1 [[COND2:%.*]], i32 [[N:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: br i1 [[COND1]], label %[[ENTRY_SPLIT_US:.*]], label %[[ENTRY_SPLIT:.*]]
; CHECK-NEXT: br i1 [[COND1]], label %[[ENTRY_SPLIT_US:.*]], label %[[ENTRY_SPLIT:.*]], !prof [[PROF1]]
; CHECK: [[ENTRY_SPLIT_US]]:
; CHECK-NEXT: br label %[[LOOP1_US:.*]]
; CHECK: [[LOOP1_US]]:
Expand All @@ -263,7 +263,7 @@ define void @test_sibling_loops(i1 %cond1, i1 %cond2, i32 %N) {
; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 false) [ "deopt"() ]
; CHECK-NEXT: unreachable
; CHECK: [[BETWEEN]]:
; CHECK-NEXT: br i1 [[COND2]], label %[[BETWEEN_SPLIT_US2:.*]], label %[[BETWEEN_SPLIT:.*]]
; CHECK-NEXT: br i1 [[COND2]], label %[[BETWEEN_SPLIT_US2:.*]], label %[[BETWEEN_SPLIT:.*]], !prof [[PROF1]]
; CHECK: [[BETWEEN_SPLIT_US2]]:
; CHECK-NEXT: br label %[[LOOP2_US:.*]]
; CHECK: [[LOOP2_US]]:
Expand Down Expand Up @@ -343,3 +343,9 @@ exit:

declare void @may_throw(i32 %i)
declare i32 @__CxxFrameHandler3(...)

!0 = !{!"function_entry_count", i32 10}
;.
; CHECK: [[PROF0]] = !{!"function_entry_count", i32 10}
; CHECK: [[PROF1]] = !{!"branch_weights", i32 1048575, i32 1}
;.