[InstCombine] Fix visitSwitchInst to use right operand types for sub cstexpr

The visitSwitchInst generates SUB constant expressions to recompute the
switch condition. When truncating the condition to a smaller type, SUB
expressions should use the previous type (before trunc) for both
operands. This fixes an assertion crash.

Differential Revision: http://reviews.llvm.org/D6644

rdar://problem/19191835

llvm-svn: 224574

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 5eee15f6489..fc965b879df 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2115,8 +2115,10 @@ Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
         for (SwitchInst::CaseIt i = SI.case_begin(), e = SI.case_end();
              i != e; ++i) {
           ConstantInt* CaseVal = i.getCaseValue();
-          Constant* NewCaseVal = ConstantExpr::getSub(cast<Constant>(CaseVal),
-                                                      AddRHS);
+          Constant *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");
           i.setValue(cast<ConstantInt>(NewCaseVal));