[GuardWidening] Fix widening possibility check

llvm/lib/Transforms/Scalar/GuardWidening.cpp

@@ -184,6 +184,7 @@ class GuardWideningImpl {
   /// Compute the score for widening the condition in \p DominatedInstr
   /// into \p WideningPoint.
   WideningScore computeWideningScore(Instruction *DominatedInstr,
+                                     Instruction *ToWiden,
                                      Instruction *WideningPoint,
                                      SmallVectorImpl<Value *> &ChecksToHoist,
                                      SmallVectorImpl<Value *> &ChecksToWiden);
@@ -423,8 +424,8 @@ bool GuardWideningImpl::eliminateInstrViaWidening(
         continue;
       SmallVector<Value *> CandidateChecks;
       parseWidenableGuard(Candidate, CandidateChecks);
-      auto Score = computeWideningScore(Instr, WideningPoint, ChecksToHoist,
-                                        CandidateChecks);
+      auto Score = computeWideningScore(Instr, Candidate, WideningPoint,
+                                        ChecksToHoist, CandidateChecks);
       LLVM_DEBUG(dbgs() << "Score between " << *Instr << " and " << *Candidate
                         << " is " << scoreTypeToString(Score) << "\n");
       if (Score > BestScoreSoFar) {
@@ -456,8 +457,8 @@ bool GuardWideningImpl::eliminateInstrViaWidening(
 }
 
 GuardWideningImpl::WideningScore GuardWideningImpl::computeWideningScore(
-    Instruction *DominatedInstr, Instruction *WideningPoint,
-    SmallVectorImpl<Value *> &ChecksToHoist,
+    Instruction *DominatedInstr, Instruction *ToWiden,
+    Instruction *WideningPoint, SmallVectorImpl<Value *> &ChecksToHoist,
     SmallVectorImpl<Value *> &ChecksToWiden) {
   Loop *DominatedInstrLoop = LI.getLoopFor(DominatedInstr->getParent());
   Loop *DominatingGuardLoop = LI.getLoopFor(WideningPoint->getParent());
@@ -475,7 +476,10 @@ GuardWideningImpl::WideningScore GuardWideningImpl::computeWideningScore(
 
   if (!canBeHoistedTo(ChecksToHoist, WideningPoint))
     return WS_IllegalOrNegative;
-  if (!canBeHoistedTo(ChecksToWiden, WideningPoint))
+  // Further in the GuardWideningImpl::hoistChecks the entire condition might be
+  // widened, not the parsed list of checks. So we need to check the possibility
+  // of that condition hoisting.
+  if (!canBeHoistedTo(getCondition(ToWiden), WideningPoint))
     return WS_IllegalOrNegative;
 
   // If the guard was conditional executed, it may never be reached

llvm/test/Transforms/GuardWidening/hoist-checks.ll

@@ -0,0 +1,45 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -passes=guard-widening < %s | FileCheck %s
+
+declare void @llvm.experimental.deoptimize.isVoid(...)
+declare i1 @llvm.experimental.widenable.condition()
+
+; In the current scheme we widen `br i1 %and1`, so we try to build
+; `and i1 poison, %and1` using `%call0` as insertion point.
+; That's not possible, so widening will not occur in the case.
+; TODO: Widen `%call0` in the test case, not a branch.
+define void @test() {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  bb0:
+; CHECK-NEXT:    [[CALL0:%.*]] = call i1 @llvm.experimental.widenable.condition()
+; CHECK-NEXT:    [[AND0:%.*]] = and i1 false, [[CALL0]]
+; CHECK-NEXT:    [[AND1:%.*]] = and i1 false, [[AND0]]
+; CHECK-NEXT:    br i1 [[AND1]], label [[BB1:%.*]], label [[DEOPT:%.*]]
+; CHECK:       bb1:
+; CHECK-NEXT:    [[CALL1:%.*]] = call i1 @llvm.experimental.widenable.condition()
+; CHECK-NEXT:    [[AND2:%.*]] = and i1 poison, [[CALL1]]
+; CHECK-NEXT:    br i1 [[AND2]], label [[UNREACH:%.*]], label [[DEOPT]]
+; CHECK:       unreach:
+; CHECK-NEXT:    unreachable
+; CHECK:       deopt:
+; CHECK-NEXT:    call void (...) @llvm.experimental.deoptimize.isVoid(i32 0) [ "deopt"(i32 0) ]
+; CHECK-NEXT:    ret void
+;
+bb0:
+  %call0 = call i1 @llvm.experimental.widenable.condition()
+  %and0 = and i1 false, %call0
+  %and1 = and i1 false, %and0
+  br i1 %and1, label %bb1, label %deopt
+
+bb1:
+  %call1 = call i1 @llvm.experimental.widenable.condition()
+  %and2 = and i1 poison, %call1
+  br i1 %and2, label %unreach, label %deopt
+
+unreach:
+  unreachable
+
+deopt:
+  call void (...) @llvm.experimental.deoptimize.isVoid(i32 0) [ "deopt"(i32 0) ]
+  ret void
+}