[PATCH] D87435: [PGO] Skip if an IndirectBrInst critical edge cannot be split

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 291003.
MaskRay added a comment.

Move the check from BreakCriticalEdges.cpp to PGOInstrumentation.cpp


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D87435/new/

https://reviews.llvm.org/D87435

Files:
  llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
  llvm/test/Transforms/PGOProfile/split-indirectbr-critical-edges.ll


Index: llvm/test/Transforms/PGOProfile/split-indirectbr-critical-edges.ll
===================================================================
--- llvm/test/Transforms/PGOProfile/split-indirectbr-critical-edges.ll
+++ llvm/test/Transforms/PGOProfile/split-indirectbr-critical-edges.ll
@@ -37,3 +37,27 @@
   indirectbr i8* %2, [label %for.cond2, label %if.end]
 ; CHECK: indirectbr i8* %2, [label %for.cond2, label %if.end]
 }
+
+;; If an indirectbr critical edge cannot be split, ignore it.
+;; The edge will not be profiled.
+; CHECK-LABEL: @cannot_split(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.instrprof.increment
+; CHECK-NOT:     call void @llvm.instrprof.increment
+define i32 @cannot_split(i8* nocapture readonly %p) {
+entry:
+  %targets = alloca <2 x i8*>, align 16
+  store <2 x i8*> <i8* blockaddress(@cannot_split, %indirect), i8* blockaddress(@cannot_split, %end)>, <2 x i8*>* %targets, align 16
+  %arrayidx2 = getelementptr inbounds i8, i8* %p, i64 1
+  %0 = load i8, i8* %arrayidx2
+  %idxprom = sext i8 %0 to i64
+  %arrayidx3 = getelementptr inbounds <2 x i8*>, <2 x i8*>* %targets, i64 0, i64 %idxprom
+  %1 = load i8*, i8** %arrayidx3, align 8
+  br label %indirect
+
+indirect:                                         ; preds = %entry, %indirect
+  indirectbr i8* %1, [label %indirect, label %end]
+
+end:                                              ; preds = %indirect
+  ret i32 0
+}
Index: llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -807,8 +807,11 @@
   if (!E->IsCritical)
     return canInstrument(DestBB);
 
+  // Some IndirectBr critical edges cannot be split by the previous
+  // SplitIndirectBrCriticalEdges call. Bail out.
   unsigned SuccNum = GetSuccessorNumber(SrcBB, DestBB);
-  BasicBlock *InstrBB = SplitCriticalEdge(TI, SuccNum);
+  BasicBlock *InstrBB =
+      isa<IndirectBrInst>(TI) ? nullptr : SplitCriticalEdge(TI, SuccNum);
   if (!InstrBB) {
     LLVM_DEBUG(
         dbgs() << "Fail to split critical edge: not instrument this edge.\n");


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D87435.291003.patch
Type: text/x-patch
Size: 2215 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200910/a7a8b01d/attachment.bin>