Reapply a fixed version of r133285.

This tightens up checking for overflow in alloca sizes, based on feedback
from Duncan and John about the change in r132926.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134749 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 5 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 601d9b42f3..036f0d3367 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -30,6 +30,14 @@ static Value *DecomposeSimpleLinearExpr(Value *Val, unsigned &Scale,
   }
   
   if (BinaryOperator *I = dyn_cast<BinaryOperator>(Val)) {
+    // Cannot look past anything that might overflow.
+    OverflowingBinaryOperator *OBI = dyn_cast<OverflowingBinaryOperator>(Val);
+    if (OBI && !OBI->hasNoUnsignedWrap()) {
+      Scale = 1;
+      Offset = 0;
+      return Val;
+    }
+
     if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
       if (I->getOpcode() == Instruction::Shl) {
         // This is a value scaled by '1 << the shift amt'.
@@ -71,11 +79,6 @@ Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI,
   // This requires TargetData to get the alloca alignment and size information.
   if (!TD) return 0;
 
-  // Insist that the amount-to-allocate not overflow.
-  OverflowingBinaryOperator *OBI =
-    dyn_cast<OverflowingBinaryOperator>(AI.getOperand(0));
-  if (OBI && !(OBI->hasNoSignedWrap() || OBI->hasNoUnsignedWrap())) return 0;
-
   const PointerType *PTy = cast<PointerType>(CI.getType());
   
   BuilderTy AllocaBuilder(*Builder);