[InstCombine] Fix constexpr issue in select combining

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.

Differential Revision: https://reviews.llvm.org/D25466

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284000 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index 54f8b722b7e95250802a1b2fc4381d311960e792..6b31a5449f74dcce8c656422c3b18a5541138660 100644 (file)
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2271,9 +2271,9 @@ Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
           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 @@ Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
              "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;
   }
 

diff --git a/test/Transforms/InstCombine/switch-constant-expr.ll b/test/Transforms/InstCombine/switch-constant-expr.ll
new file mode 100644 (file)
index 0000000..c2ea83b
--- /dev/null
+++ b/test/Transforms/InstCombine/switch-constant-expr.ll
@@ -0,0 +1,44 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+@g = global i32 0
+
+; PR30486
+define i32 @single_case() {
+; CHECK-LABEL: @single_case(
+; 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
+}
+
+define i32 @multiple_cases() {
+; CHECK-LABEL: @multiple_cases(
+; CHECK-NEXT:    switch i32 ptrtoint (i32* @g to i32), label %x [
+; CHECK-NEXT:    i32 2, label %one
+; CHECK-NEXT:    i32 3, label %two
+; CHECK-NEXT:    ]
+; CHECK:       x:
+; CHECK-NEXT:    ret i32 0
+; CHECK:       one:
+; CHECK-NEXT:    ret i32 1
+; CHECK:       two:
+; CHECK-NEXT:    ret i32 2
+;
+  switch i32 add (i32 ptrtoint (i32* @g to i32), i32 -1), label %x [
+  i32 1, label %one
+  i32 2, label %two
+  ]
+x:
+  ret i32 0
+
+one:
+  ret i32 1
+
+two:
+  ret i32 2
+}