[llvm] r224588 - Reapply: [InstCombine] Fix visitSwitchInst to use right operand types for sub cstexpr

[Bruno Cardoso Lopes]

Author: bruno
Date: Fri Dec 19 11:12:35 2014
New Revision: 224588

URL: http://llvm.org/viewvc/llvm-project?rev=224588&view=rev
Log:
Reapply: [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. Also, fix code to also return the modified switch when only
the truncation is performed.

This fixes an assertion crash.

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

rdar://problem/19191835

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
    llvm/trunk/test/Transforms/InstCombine/narrow-switch.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp?rev=224588&r1=224587&r2=224588&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp Fri Dec 19 11:12:35 2014
@@ -2095,8 +2095,10 @@ Instruction *InstCombiner::visitSwitchIn
   // the largest legal integer type. We need to be conservative here since
   // x86 generates redundant zero-extenstion instructions if the operand is
   // truncated to i8 or i16.
+  bool TruncCond = false;
   if (DL && BitWidth > NewWidth &&
       NewWidth >= DL->getLargestLegalIntTypeSize()) {
+    TruncCond = true;
     IntegerType *Ty = IntegerType::get(SI.getContext(), NewWidth);
     Builder->SetInsertPoint(&SI);
     Value *NewCond = Builder->CreateTrunc(SI.getCondition(), Ty, "trunc");
@@ -2115,8 +2117,12 @@ Instruction *InstCombiner::visitSwitchIn
         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 = CaseVal;
+          if (TruncCond)
+            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));
@@ -2126,7 +2132,8 @@ Instruction *InstCombiner::visitSwitchIn
         return &SI;
       }
   }
-  return nullptr;
+
+  return TruncCond ? &SI : nullptr;
 }
 
 Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {

Modified: llvm/trunk/test/Transforms/InstCombine/narrow-switch.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/narrow-switch.ll?rev=224588&r1=224587&r2=224588&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/narrow-switch.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/narrow-switch.ll Fri Dec 19 11:12:35 2014
@@ -91,3 +91,33 @@ return:
   %retval.0 = phi i32 [ 24, %sw.default ], [ 123, %sw.bb2 ], [ 213, %sw.bb1 ], [ 231, %entry ]
   ret i32 %retval.0
 }
+
+; Make sure to avoid assertion crashes and use the type before
+; truncation to generate the sub constant expressions that leads
+; to the recomputed condition.
+;
+; CHECK-LABEL: @trunc64to59
+; CHECK: switch i59
+; CHECK: i59 0, label
+; CHECK: i59 18717182647723699, label
+
+define void @trunc64to59(i64 %a) {
+entry:
+  %tmp0 = and i64 %a, 15
+  %tmp1 = mul i64 %tmp0, -6425668444178048401
+  %tmp2 = add i64 %tmp1, 5170979678563097242
+  %tmp3 = mul i64 %tmp2, 1627972535142754813
+  switch i64 %tmp3, label %sw.default [
+    i64 847514119312061490, label %sw.bb1
+    i64 866231301959785189, label %sw.bb2
+  ]
+
+sw.bb1:
+  br label %sw.default
+
+sw.bb2:
+  br label %sw.default
+
+sw.default:
+  ret void
+}