[llvm] 5ae8a9b - [SimplifyCfg] Handle trunc nuw i1 condition in Equality comparison. (#153051)

[via llvm-commits]

Author: Andreas Jonson
Date: 2025-08-17T09:53:40+02:00
New Revision: 5ae8a9b8cee3d4477fdec107a3ab29b633ec4f9f

URL: https://github.com/llvm/llvm-project/commit/5ae8a9b8cee3d4477fdec107a3ab29b633ec4f9f
DIFF: https://github.com/llvm/llvm-project/commit/5ae8a9b8cee3d4477fdec107a3ab29b633ec4f9f.diff

LOG: [SimplifyCfg] Handle trunc nuw i1 condition in Equality comparison. (#153051)

proof: https://alive2.llvm.org/ce/z/WVt4-F

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/SimplifyCFG.cpp
    llvm/test/Transforms/SimplifyCFG/switch_create.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 1436e479ba091..46d6c2a541a8c 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -810,11 +810,15 @@ Value *SimplifyCFGOpt::isValueEqualityComparison(Instruction *TI) {
     if (!SI->getParent()->hasNPredecessorsOrMore(128 / SI->getNumSuccessors()))
       CV = SI->getCondition();
   } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
-    if (BI->isConditional() && BI->getCondition()->hasOneUse())
+    if (BI->isConditional() && BI->getCondition()->hasOneUse()) {
       if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
         if (ICI->isEquality() && getConstantInt(ICI->getOperand(1), DL))
           CV = ICI->getOperand(0);
+      } else if (auto *Trunc = dyn_cast<TruncInst>(BI->getCondition())) {
+        if (Trunc->hasNoUnsignedWrap())
+          CV = Trunc->getOperand(0);
       }
+    }
 
   // Unwrap any lossless ptrtoint cast.
   if (CV) {
@@ -840,11 +844,20 @@ BasicBlock *SimplifyCFGOpt::getValueEqualityComparisonCases(
   }
 
   BranchInst *BI = cast<BranchInst>(TI);
-  ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
-  BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE);
-  Cases.push_back(ValueEqualityComparisonCase(
-      getConstantInt(ICI->getOperand(1), DL), Succ));
-  return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
+  Value *Cond = BI->getCondition();
+  ICmpInst::Predicate Pred;
+  ConstantInt *C;
+  if (auto *ICI = dyn_cast<ICmpInst>(Cond)) {
+    Pred = ICI->getPredicate();
+    C = getConstantInt(ICI->getOperand(1), DL);
+  } else {
+    Pred = ICmpInst::ICMP_NE;
+    auto *Trunc = cast<TruncInst>(Cond);
+    C = ConstantInt::get(cast<IntegerType>(Trunc->getOperand(0)->getType()), 0);
+  }
+  BasicBlock *Succ = BI->getSuccessor(Pred == ICmpInst::ICMP_NE);
+  Cases.push_back(ValueEqualityComparisonCase(C, Succ));
+  return BI->getSuccessor(Pred == ICmpInst::ICMP_EQ);
 }
 
 /// Given a vector of bb/value pairs, remove any entries
@@ -1106,7 +1119,10 @@ static void getBranchWeights(Instruction *TI,
   // default weight to be the first entry.
   if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
     assert(Weights.size() == 2);
-    ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
+    auto *ICI = dyn_cast<ICmpInst>(BI->getCondition());
+    if (!ICI)
+      return;
+
     if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
       std::swap(Weights.front(), Weights.back());
   }

diff  --git a/llvm/test/Transforms/SimplifyCFG/switch_create.ll b/llvm/test/Transforms/SimplifyCFG/switch_create.ll
index f446d718f8206..a1533bdcffb43 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch_create.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch_create.ll
@@ -1068,3 +1068,60 @@ if:
 else:
   ret void
 }
+
+define void @trunc_nuw_i1_condition(i32 %V) {
+; CHECK-LABEL: @trunc_nuw_i1_condition(
+; CHECK-NEXT:    switch i32 [[V:%.*]], label [[F:%.*]] [
+; CHECK-NEXT:      i32 2, label [[T:%.*]]
+; CHECK-NEXT:      i32 0, label [[T]]
+; CHECK-NEXT:    ]
+; CHECK:       common.ret:
+; CHECK-NEXT:    ret void
+; CHECK:       T:
+; CHECK-NEXT:    call void @foo1()
+; CHECK-NEXT:    br label [[COMMON_RET:%.*]]
+; CHECK:       F:
+; CHECK-NEXT:    call void @foo2()
+; CHECK-NEXT:    br label [[COMMON_RET]]
+;
+  %C1 = icmp eq i32 %V, 2
+  br i1 %C1, label %T, label %N
+N:
+  %C2 = trunc nuw i32 %V to i1
+  br i1 %C2, label %F, label %T
+T:
+  call void @foo1( )
+  ret void
+F:
+  call void @foo2( )
+  ret void
+}
+
+define void @neg_trunc_i1_condition(i32 %V) {
+; CHECK-LABEL: @neg_trunc_i1_condition(
+; CHECK-NEXT:    [[C1:%.*]] = icmp ne i32 [[V:%.*]], 2
+; CHECK-NEXT:    [[C2:%.*]] = trunc i32 [[V]] to i1
+; CHECK-NEXT:    [[OR_COND:%.*]] = and i1 [[C1]], [[C2]]
+; CHECK-NEXT:    br i1 [[OR_COND]], label [[F:%.*]], label [[T:%.*]]
+; CHECK:       common.ret:
+; CHECK-NEXT:    ret void
+; CHECK:       T:
+; CHECK-NEXT:    call void @foo1()
+; CHECK-NEXT:    br label [[COMMON_RET:%.*]]
+; CHECK:       F:
+; CHECK-NEXT:    call void @foo2()
+; CHECK-NEXT:    br label [[COMMON_RET]]
+;
+  %C1 = icmp eq i32 %V, 2
+  br i1 %C1, label %T, label %N
+N:
+  %C2 = trunc i32 %V to i1
+  br i1 %C2, label %F, label %T
+T:
+  call void @foo1( )
+  ret void
+F:
+  call void @foo2( )
+  ret void
+}
+