[InstCombine] Fix worklist management when removing guard intrinsic

When multiple guard intrinsics are merged into one, currently the
result of eraseInstFromFunction() is returned -- however, this
should only be done if the current instruction is being removed.
In this case we're removing a different instruction and should
instead report that the current one has been modified by returning it.

For this test case, this reduces the number of instcombine iterations
from 5 to 2 (the minimum possible).

Differential Revision: https://reviews.llvm.org/D72558

1 files changed, 10 insertions, 10 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index bcbc953ecd6..f463c5fa113 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -4179,18 +4179,18 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
       Value *CurrCond = II->getArgOperand(0);
 
       // Remove a guard that it is immediately preceded by an identical guard.
-      if (CurrCond == NextCond)
-        return eraseInstFromFunction(*NextInst);
-
       // Otherwise canonicalize guard(a); guard(b) -> guard(a & b).
-      Instruction *MoveI = II->getNextNonDebugInstruction();
-      while (MoveI != NextInst) {
-        auto *Temp = MoveI;
-        MoveI = MoveI->getNextNonDebugInstruction();
-        Temp->moveBefore(II);
+      if (CurrCond != NextCond) {
+        Instruction *MoveI = II->getNextNonDebugInstruction();
+        while (MoveI != NextInst) {
+          auto *Temp = MoveI;
+          MoveI = MoveI->getNextNonDebugInstruction();
+          Temp->moveBefore(II);
+        }
+        II->setArgOperand(0, Builder.CreateAnd(CurrCond, NextCond));
       }
-      II->setArgOperand(0, Builder.CreateAnd(CurrCond, NextCond));
-      return eraseInstFromFunction(*NextInst);
+      eraseInstFromFunction(*NextInst);
+      return II;
     }
     break;
   }