[InstCombine] fix bug when offsetting case values of a switch (PR31260)

We could truncate the condition and then try to fold the add into the
original condition value causing wrong case constants to be used.

Move the offset transform ahead of the truncate transform and return
after each transform, so there's no chance of getting confused values.

Fix for:
https://llvm.org/bugs/show_bug.cgi?id=31260

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@289442 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index f96766db6dfb7e313ab45825083b2f320f9ac8d1..0d29c1dceea1da91c0c6b955bf9ce67b0b9c98f7 100644 (file)
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2232,6 +2232,20 @@ Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
 
 Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
   Value *Cond = SI.getCondition();
+  Value *Op0;
+  ConstantInt *AddRHS;
+  if (match(Cond, m_Add(m_Value(Op0), m_ConstantInt(AddRHS)))) {
+    // Change 'switch (X+4) case 1:' into 'switch (X) case -3'.
+    for (SwitchInst::CaseIt CaseIter : SI.cases()) {
+      Constant *NewCase = ConstantExpr::getSub(CaseIter.getCaseValue(), AddRHS);
+      assert(isa<ConstantInt>(NewCase) &&
+             "Result of expression should be constant");
+      CaseIter.setValue(cast<ConstantInt>(NewCase));
+    }
+    SI.setCondition(Op0);
+    return &SI;
+  }
+
   unsigned BitWidth = cast<IntegerType>(Cond->getType())->getBitWidth();
   APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
   computeKnownBits(Cond, KnownZero, KnownOne, 0, &SI);
@@ -2252,9 +2266,7 @@ Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
   // Shrink the condition operand if the new type is smaller than the old type.
   // This may produce a non-standard type for the switch, but that's ok because
   // the backend should extend back to a legal type for the target.
-  bool TruncCond = false;
   if (NewWidth > 0 && NewWidth < BitWidth) {
-    TruncCond = true;
     IntegerType *Ty = IntegerType::get(SI.getContext(), NewWidth);
     Builder->SetInsertPoint(&SI);
     Value *NewCond = Builder->CreateTrunc(Cond, Ty, "trunc");
@@ -2264,32 +2276,10 @@ Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
       APInt TruncatedCase = CaseIter.getCaseValue()->getValue().trunc(NewWidth);
       CaseIter.setValue(ConstantInt::get(SI.getContext(), TruncatedCase));
     }
-  }
-
-  Value *Op0 = nullptr;
-  ConstantInt *AddRHS = nullptr;
-  if (match(Cond, m_Add(m_Value(Op0), m_ConstantInt(AddRHS)))) {
-    // Change 'switch (X+4) case 1:' into 'switch (X) case -3'.
-    for (SwitchInst::CaseIt CaseIter : SI.cases()) {
-      ConstantInt *CaseVal = CaseIter.getCaseValue();
-      Constant *LHS = CaseVal;
-      if (TruncCond) {
-        LHS = LeadingKnownZeros
-                  ? ConstantExpr::getZExt(CaseVal, Cond->getType())
-                  : ConstantExpr::getSExt(CaseVal, Cond->getType());
-      }
-      Constant *NewCaseVal = ConstantExpr::getSub(LHS, AddRHS);
-      assert(isa<ConstantInt>(NewCaseVal) &&
-             "Result of expression should be constant");
-      CaseIter.setValue(cast<ConstantInt>(NewCaseVal));
-    }
-    SI.setCondition(Op0);
-    if (auto *CondI = dyn_cast<Instruction>(Cond))
-      Worklist.Add(CondI);
     return &SI;
   }
 
-  return TruncCond ? &SI : nullptr;
+  return nullptr;
 }
 
 Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {

diff --git a/test/Transforms/InstCombine/narrow-switch.ll b/test/Transforms/InstCombine/narrow-switch.ll
index e58b49565689e6d27d1b3d4cf7a579da133d7a5b..8f4c24b9debf6be47404ec31765c8939dddc4956 100644 (file)
--- a/test/Transforms/InstCombine/narrow-switch.ll
+++ b/test/Transforms/InstCombine/narrow-switch.ll
@@ -135,10 +135,11 @@ sw.default:
 define i8 @PR31260(i8 %x) {
 ; ALL-LABEL: @PR31260(
 ; ALL-NEXT:  entry:
-; ALL-NEXT:    [[T4:%.*]] = and i8 %x, 2
-; ALL-NEXT:    switch i8 [[T4]], label %exit [
-; ALL-NEXT:    i8 -128, label %case126
-; ALL-NEXT:    i8 -126, label %case124
+; ALL-NEXT:    [[TMP0:%.*]] = trunc i8 %x to i2
+; ALL-NEXT:    [[TRUNC:%.*]] = and i2 [[TMP0]], -2
+; ALL-NEXT:    switch i2 [[TRUNC]], label %exit [
+; ALL-NEXT:    i2 0, label %case126
+; ALL-NEXT:    i2 -2, label %case124
 ; ALL-NEXT:    ]
 ; ALL:       exit:
 ; ALL-NEXT:    ret i8 1