[llvm] 38a64aa - [ControlHeightReduction] Don't combine a "poison" branch

[Kazu Hirata via llvm-commits]

Author: Kazu Hirata
Date: 2023-02-28T16:13:30-08:00
New Revision: 38a64aab4a3fbaaeb383638ff654247902796556

URL: https://github.com/llvm/llvm-project/commit/38a64aab4a3fbaaeb383638ff654247902796556
DIFF: https://github.com/llvm/llvm-project/commit/38a64aab4a3fbaaeb383638ff654247902796556.diff

LOG: [ControlHeightReduction] Don't combine a "poison" branch

Without this patch, the control height reduction pass would combine a
"poison" branch with an earlier well-defined branch, turning the
earlier branch into a "poison" branch also.

This patch fixes the problem by rejecting "poison" conditional
branches.

Differential Revision: https://reviews.llvm.org/D145008

Added: 
    llvm/test/Transforms/PGOProfile/chr-poison.ll

Modified: 
    llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp b/llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp
index 83e662906bceb..5b458f539228e 100644
--- a/llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp
+++ b/llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp
@@ -631,7 +631,7 @@ static bool checkBiasedBranch(BranchInst *BI, Region *R,
                               DenseSet<Region *> &TrueBiasedRegionsGlobal,
                               DenseSet<Region *> &FalseBiasedRegionsGlobal,
                               DenseMap<Region *, BranchProbability> &BranchBiasMap) {
-  if (!BI->isConditional())
+  if (!BI->isConditional() || isa<PoisonValue>(BI->getCondition()))
     return false;
   BranchProbability ThenProb, ElseProb;
   if (!extractBranchProbabilities(BI, ThenProb, ElseProb))

diff  --git a/llvm/test/Transforms/PGOProfile/chr-poison.ll b/llvm/test/Transforms/PGOProfile/chr-poison.ll
new file mode 100644
index 0000000000000..ddc74ff60c751
--- /dev/null
+++ b/llvm/test/Transforms/PGOProfile/chr-poison.ll
@@ -0,0 +1,76 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes='require<profile-summary>,function(chr)' -S | FileCheck %s
+
+; Make sure nothing happens.  We must not combine a "poison" branch
+; with any other branch.
+define void @chr_poison(i1 %arg) !prof !29 {
+; CHECK-LABEL: @chr_poison(
+; CHECK-NEXT:    br i1 false, label [[BB3:%.*]], label [[BB2:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    ret void
+; CHECK:       bb3:
+; CHECK-NEXT:    br i1 poison, label [[BB5:%.*]], label [[BB4:%.*]], !prof [[PROF30:![0-9]+]]
+; CHECK:       bb4:
+; CHECK-NEXT:    br label [[BB5]]
+; CHECK:       bb5:
+; CHECK-NEXT:    br i1 [[ARG:%.*]], label [[BB2]], label [[BB6:%.*]], !prof [[PROF31:![0-9]+]]
+; CHECK:       bb6:
+; CHECK-NEXT:    br label [[BB2]]
+; CHECK:       bb7:
+; CHECK-NEXT:    br label [[BB5]]
+;
+  br i1 false, label %bb3, label %bb2
+
+bb2:
+  ret void
+
+bb3:
+  br i1 poison, label %bb5, label %bb4, !prof !30
+
+bb4:
+  br label %bb5
+
+bb5:
+  br i1 %arg, label %bb2, label %bb6, !prof !31
+
+bb6:
+  br label %bb2
+
+bb7:
+  br label %bb5
+}
+
+!llvm.module.flags = !{!0}
+
+!0 = !{i32 1, !"ProfileSummary", !1}
+!1 = !{!2, !3, !4, !5, !6, !7, !8, !9, !10, !11}
+!2 = !{!"ProfileFormat", !"SampleProfile"}
+!3 = !{!"TotalCount", i64 2625732223}
+!4 = !{!"MaxCount", i64 6099111}
+!5 = !{!"MaxInternalCount", i64 0}
+!6 = !{!"MaxFunctionCount", i64 8812263}
+!7 = !{!"NumCounts", i64 1399554}
+!8 = !{!"NumFunctions", i64 14940}
+!9 = !{!"IsPartialProfile", i64 0}
+!10 = !{!"PartialProfileRatio", double 0.000000e+00}
+!11 = !{!"DetailedSummary", !12}
+!12 = !{!13, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !28}
+!13 = !{i32 10000, i64 6099103, i32 8}
+!14 = !{i32 100000, i64 6083920, i32 44}
+!15 = !{i32 200000, i64 5615450, i32 92}
+!16 = !{i32 300000, i64 658615, i32 301}
+!17 = !{i32 400000, i64 276706, i32 1049}
+!18 = !{i32 500000, i64 224143, i32 2110}
+!19 = !{i32 600000, i64 155027, i32 3480}
+!20 = !{i32 700000, i64 62158, i32 6258}
+!21 = !{i32 800000, i64 29875, i32 12602}
+!22 = !{i32 900000, i64 5684, i32 34979}
+!23 = !{i32 950000, i64 1439, i32 81728}
+!24 = !{i32 990000, i64 319, i32 227620}
+!25 = !{i32 999000, i64 34, i32 416158}
+!26 = !{i32 999900, i64 4, i32 603970}
+!27 = !{i32 999990, i64 1, i32 750171}
+!28 = !{i32 999999, i64 1, i32 750171}
+!29 = !{!"function_entry_count", i64 3204}
+!30 = !{!"branch_weights", i32 2126980204, i32 20503444}
+!31 = !{!"branch_weights", i32 997, i32 2}