ConstantFold: Fix big shift constant folding

Constant folding for shift IR instructions ignores all bits above 32 of
second argument (shift amount).
Because of that, some undef results are not recognized and APInt can
raise an assert failure if second argument has more than 64 bits.

Patch by Paweł Bylica!

Differential Revision: http://reviews.llvm.org/D7701

llvm-svn: 232176

1 files changed, 12 insertions, 21 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index cf7f3705fb7..d97d2c4a702 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1120,27 +1120,18 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
         return ConstantInt::get(CI1->getContext(), C1V | C2V);
       case Instruction::Xor:
         return ConstantInt::get(CI1->getContext(), C1V ^ C2V);
-      case Instruction::Shl: {
-        uint32_t shiftAmt = C2V.getZExtValue();
-        if (shiftAmt < C1V.getBitWidth())
-          return ConstantInt::get(CI1->getContext(), C1V.shl(shiftAmt));
-        else
-          return UndefValue::get(C1->getType()); // too big shift is undef
-      }
-      case Instruction::LShr: {
-        uint32_t shiftAmt = C2V.getZExtValue();
-        if (shiftAmt < C1V.getBitWidth())
-          return ConstantInt::get(CI1->getContext(), C1V.lshr(shiftAmt));
-        else
-          return UndefValue::get(C1->getType()); // too big shift is undef
-      }
-      case Instruction::AShr: {
-        uint32_t shiftAmt = C2V.getZExtValue();
-        if (shiftAmt < C1V.getBitWidth())
-          return ConstantInt::get(CI1->getContext(), C1V.ashr(shiftAmt));
-        else
-          return UndefValue::get(C1->getType()); // too big shift is undef
-      }
+      case Instruction::Shl:
+        if (C2V.ult(C1V.getBitWidth()))
+          return ConstantInt::get(CI1->getContext(), C1V.shl(C2V));
+        return UndefValue::get(C1->getType()); // too big shift is undef
+      case Instruction::LShr:
+        if (C2V.ult(C1V.getBitWidth()))
+          return ConstantInt::get(CI1->getContext(), C1V.lshr(C2V));
+        return UndefValue::get(C1->getType()); // too big shift is undef
+      case Instruction::AShr:
+        if (C2V.ult(C1V.getBitWidth()))
+          return ConstantInt::get(CI1->getContext(), C1V.ashr(C2V));
+        return UndefValue::get(C1->getType()); // too big shift is undef
       }
     }