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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224588 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index 5eee15f648906cc4997e03a8aaf7ea002cf50063..898e5708ff1585abb8341b05045e42868b48d4e6 100644 (file)
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2095,8 +2095,10 @@ Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
   // 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::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 = 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::visitSwitchInst(SwitchInst &SI) {
         return &SI;
       }
   }
-  return nullptr;
+
+  return TruncCond ? &SI : nullptr;
 }
 
 Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {

diff --git a/test/Transforms/InstCombine/narrow-switch.ll b/test/Transforms/InstCombine/narrow-switch.ll
index 7646189b8540f93102c48e57457857ed359f757c..f3f19bae03dda75e7118b5bc3e88628fde68f939 100644 (file)
--- a/test/Transforms/InstCombine/narrow-switch.ll
+++ b/test/Transforms/InstCombine/narrow-switch.ll
@@ -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
+}