[PATCH] D72558: [InstCombine] Fix worklist management when removing guard intrinsic

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: reames, spatel, lebedev.ri.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

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).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72558

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
  llvm/test/Transforms/InstCombine/call-guard.ll


Index: llvm/test/Transforms/InstCombine/call-guard.ll
===================================================================
--- llvm/test/Transforms/InstCombine/call-guard.ll
+++ llvm/test/Transforms/InstCombine/call-guard.ll
@@ -1,4 +1,4 @@
-; RUN: opt < %s -instcombine -S | FileCheck %s
+; RUN: opt < %s -instcombine -instcombine-infinite-loop-threshold=2 -S | FileCheck %s
 ; RUN: opt < %s -instcombine -S -debugify-each | FileCheck %s
 
 declare void @llvm.experimental.guard(i1, ...)
Index: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -4179,18 +4179,18 @@
       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;
   }


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