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!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194840 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 0 deletions

diff --git a/include/llvm/CodeGen/FastISel.h b/include/llvm/CodeGen/FastISel.h
index 0063474534..1e0ef6b545 100644
--- a/include/llvm/CodeGen/FastISel.h
+++ b/include/llvm/CodeGen/FastISel.h
@@ -358,6 +358,15 @@ protected:
     return 0;
   }
 
+  /// \brief Check if \c Add is an add that can be safely folded into \c GEP.
+  ///
+  /// \c Add can be folded into \c GEP if:
+  /// - \c Add is an add,
+  /// - \c Add's size matches \c GEP's,
+  /// - \c Add is in the same basic block as \c GEP, and
+  /// - \c Add has a constant operand.
+  bool canFoldAddIntoGEP(const User *GEP, const Value *Add);
+
 private:
   bool SelectBinaryOp(const User *I, unsigned ISDOpcode);