[PATCH] D107935: [InstCombine] Avoid folding GEPs across loop boundaries

[Roman Lebedev via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG9cae598f8b64: [InstCombine] Avoid folding GEPs across loop boundaries (authored by clin1, committed by lebedev.ri).

Changed prior to commit:
  https://reviews.llvm.org/D107935?vs=365870&id=367538#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D107935/new/

https://reviews.llvm.org/D107935

Files:
  llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
  llvm/test/Transforms/InstCombine/gep-combine-loop-invariant.ll


Index: llvm/test/Transforms/InstCombine/gep-combine-loop-invariant.ll
===================================================================
--- llvm/test/Transforms/InstCombine/gep-combine-loop-invariant.ll
+++ llvm/test/Transforms/InstCombine/gep-combine-loop-invariant.ll
@@ -216,6 +216,7 @@
 ; CHECK-LABEL: @gep_cross_loop(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP0:%.*]] = load i64, i64* [[_ARG_:%.*]], align 8
+; CHECK-NEXT:    [[ADD_PTR:%.*]] = getelementptr inbounds float, float* [[_ARG_3:%.*]], i64 [[TMP0]]
 ; CHECK-NEXT:    br label [[FOR_COND_I:%.*]]
 ; CHECK:       for.cond.i:
 ; CHECK-NEXT:    [[IDX:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[ADD11_I:%.*]], [[FOR_BODY_I:%.*]] ]
@@ -225,8 +226,7 @@
 ; CHECK:       for.cond.i.i.i.preheader:
 ; CHECK-NEXT:    ret float [[SUM]]
 ; CHECK:       for.body.i:
-; CHECK-NEXT:    [[ARRAYIDX_I84_I_IDX:%.*]] = add nsw i64 [[IDX]], [[TMP0]]
-; CHECK-NEXT:    [[ARRAYIDX_I84_I:%.*]] = getelementptr inbounds float, float* [[_ARG_3:%.*]], i64 [[ARRAYIDX_I84_I_IDX]]
+; CHECK-NEXT:    [[ARRAYIDX_I84_I:%.*]] = getelementptr inbounds float, float* [[ADD_PTR]], i64 [[IDX]]
 ; CHECK-NEXT:    [[TMP1:%.*]] = load float, float* [[ARRAYIDX_I84_I]], align 4
 ; CHECK-NEXT:    [[ADD_I]] = fadd fast float [[SUM]], [[TMP1]]
 ; CHECK-NEXT:    [[ADD11_I]] = add nuw nsw i64 [[IDX]], 1
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2132,8 +2132,17 @@
         }
       }
 
+      // Guard the gep(gep) fold so we don't create an add inside a loop
+      // when there wasn't an equivalent instruction there before.
+      bool DifferentLoops = false;
+      if (LI)
+        if (auto *GEPLoop = LI->getLoopFor(GEP.getParent()))
+          if (auto *SrcOpI = dyn_cast<Instruction>(Src))
+            if (LI->getLoopFor(SrcOpI->getParent()) != GEPLoop)
+              DifferentLoops = true;
+
       // Fold (gep(gep(Ptr,Idx0),Idx1) -> gep(Ptr,add(Idx0,Idx1))
-      if (GO1->getType() == SO1->getType()) {
+      if (!DifferentLoops && GO1->getType() == SO1->getType()) {
         bool NewInBounds = GEP.isInBounds() && Src->isInBounds();
         auto *NewIdx =
             Builder.CreateAdd(GO1, SO1, GEP.getName() + ".idx",


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