Avoid illegal integer promotion in fastisel

Stop folding constant adds into GEP when the type size doesn't match.
Otherwise, the adds' operands are effectively being promoted, changing the
conditions of an overflow.  Results are different when:

    sext(a) + sext(b) != sext(a + b)

Problem originally found on x86-64, but also fixed issues with ARM and PPC,
which used similar code.

<rdar://problem/15292280>

Patch by Duncan Exon Smith!

llvm-svn: 194840

1 files changed, 2 insertions, 7 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCFastISel.cpp b/llvm/lib/Target/PowerPC/PPCFastISel.cpp
index 4f8e6c1a101..09117e7ded4 100644
--- a/llvm/lib/Target/PowerPC/PPCFastISel.cpp
+++ b/llvm/lib/Target/PowerPC/PPCFastISel.cpp
@@ -336,13 +336,8 @@ bool PPCFastISel::PPCComputeAddress(const Value *Obj, Address &Addr) {
               TmpOffset += CI->getSExtValue() * S;
               break;
             }
-            if (isa<AddOperator>(Op) &&
-                (!isa<Instruction>(Op) ||
-                 FuncInfo.MBBMap[cast<Instruction>(Op)->getParent()]
-                 == FuncInfo.MBB) &&
-                isa<ConstantInt>(cast<AddOperator>(Op)->getOperand(1))) {
-              // An add (in the same block) with a constant operand. Fold the
-              // constant.
+            if (canFoldAddIntoGEP(U, Op)) {
+              // A compatible add with a constant operand. Fold the constant.
               ConstantInt *CI =
               cast<ConstantInt>(cast<AddOperator>(Op)->getOperand(1));
               TmpOffset += CI->getSExtValue() * S;