[PATCH] D25466: [InstCombine] Fix constexpr issue in select combining

[Simon Pilgrim via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: majnemer, bogner, andreadb, spatel.
RKSimon added a subscriber: llvm-commits.
RKSimon set the repository for this revision to rL LLVM.

As discussed by Andrea on PR30486, we have an unsafe cast to an Instruction type in the select combine which doesn't take into account that it could be a ConstantExpr instead.


Repository:
  rL LLVM

https://reviews.llvm.org/D25466

Files:
  lib/Transforms/InstCombine/InstructionCombining.cpp
  test/Transforms/InstCombine/switch-constant-expr.ll


Index: test/Transforms/InstCombine/switch-constant-expr.ll
===================================================================
--- test/Transforms/InstCombine/switch-constant-expr.ll
+++ test/Transforms/InstCombine/switch-constant-expr.ll
@@ -0,0 +1,17 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+ at g = global i32 0
+
+; PR30486
+define i32 @func() {
+; CHECK-LABEL: @func(
+; CHECK-NEXT:    switch i32 ptrtoint (i32* @g to i32), label %x [
+; CHECK-NEXT:    ]
+; CHECK:       x:
+; CHECK-NEXT:    ret i32 0
+;
+  switch i32 add (i32 ptrtoint (i32* @g to i32), i32 -1), label %x []
+x:
+  ret i32 0
+}
Index: lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- lib/Transforms/InstCombine/InstructionCombining.cpp
+++ lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2271,9 +2271,9 @@
           SI.getContext(), C.getCaseValue()->getValue().trunc(NewWidth)));
   }
 
+  Value *Op0 = nullptr;
   ConstantInt *AddRHS = nullptr;
-  if (match(Cond, m_Add(m_Value(), m_ConstantInt(AddRHS)))) {
-    Instruction *I = cast<Instruction>(Cond);
+  if (match(Cond, m_Add(m_Value(Op0), m_ConstantInt(AddRHS)))) {
     // Change 'switch (X+4) case 1:' into 'switch (X) case -3'.
     for (SwitchInst::CaseIt i = SI.case_begin(), e = SI.case_end(); i != e;
          ++i) {
@@ -2289,8 +2289,9 @@
              "Result of expression should be constant");
       i.setValue(cast<ConstantInt>(NewCaseVal));
     }
-    SI.setCondition(I->getOperand(0));
-    Worklist.Add(I);
+    SI.setCondition(Op0);
+    if (auto *CondI = dyn_cast<Instruction>(Cond))
+      Worklist.Add(CondI);
     return &SI;
   }
 


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