[LoopPeel] Clear dispositions after peeling

[nikic]

Summary

Block dispositions of values defined inside the loop may change during peeling, so clear them. We already do this for other kind of unrolling.

[uabelho]

I've verified this fixes the problem I saw. Great!

llvm/test/Transforms/LoopUnroll/loop-block-disposition-after-loop-peeling.ll

3

Perhaps add -verify-scev since that's what caught the error? As far as I can see the actual ll output is identical with/without the fix so without -verify-scev I guess it only tests the fix in EXPENSIVE_CHECKS builds?

[nikic]

Add -verify-scev.

llvm/test/Transforms/LoopUnroll/loop-block-disposition-after-loop-peeling.ll

3

Ooops, that was just an oversight on my part.

[nikic]

Ping :)

[nikic]

Ping ;)

[nikic]

Ping

[fhahn]

LGTM, thanks!

llvm/lib/Transforms/Utils/LoopPeel.cpp

if (auto Peeled = getOptionalIntLoopAttribute(L, PeeledCountMetaData))
     AlreadyPeeled = *Peeled;
   addStringMetadataToLoop(L, PeeledCountMetaData, AlreadyPeeled + PeelCount);
 
   if (Loop *ParentLoop = L->getParentLoop())
     L = ParentLoop;
 
   // We modified the loop, update SE.
   SE->forgetTopmostLoop(L);
+  SE->forgetBlockAndLoopDispositions();
 
 #ifdef EXPENSIVE_CHECKS
   // Finally DomtTree must be correct.
   assert(DT.verify(DominatorTree::VerificationLevel::Fast));
 #endif
 
   // FIXME: Incrementally update loop-simplify
   simplifyLoop(L, &DT, LI, SE, AC, nullptr, PreserveLCSSA);
 
   NumPeeled++;
 
   return true;
 }

llvm/test/Transforms/LoopUnroll/loop-block-disposition-after-loop-peeling.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+; RUN: opt -S -passes='print<scalar-evolution>,loop(loop-unroll-full)' -verify-scev < %s 2>/dev/null | FileCheck %s
+
+define i32 @test(ptr %arg) {
+; CHECK-LABEL: define i32 @test
+; CHECK-SAME: (ptr [[ARG:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP_PEEL_BEGIN:%.*]]
+; CHECK:       loop.peel.begin:
+; CHECK-NEXT:    br label [[LOOP_PEEL:%.*]]
+; CHECK:       loop.peel:
+; CHECK-NEXT:    [[LOAD_PEEL:%.*]] = load i32, ptr null, align 4
+; CHECK-NEXT:    br i1 false, label [[LOOP_EXIT:%.*]], label [[LOOP_LATCH_PEEL:%.*]]
+; CHECK:       loop.latch.peel:
+; CHECK-NEXT:    br i1 false, label [[LOOP_EXIT]], label [[LOOP_PEEL_NEXT:%.*]]
+; CHECK:       loop.peel.next:
+; CHECK-NEXT:    br label [[LOOP_PEEL_NEXT1:%.*]]
+; CHECK:       loop.peel.next1:
+; CHECK-NEXT:    br label [[ENTRY_PEEL_NEWPH:%.*]]
+; CHECK:       entry.peel.newph:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[LOAD:%.*]] = load i32, ptr null, align 4
+; CHECK-NEXT:    br i1 false, label [[LOOP_EXIT_LOOPEXIT:%.*]], label [[LOOP_LATCH:%.*]]
+; CHECK:       loop.latch:
+; CHECK-NEXT:    br i1 false, label [[LOOP_EXIT_LOOPEXIT]], label [[LOOP]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       loop.exit.loopexit:
+; CHECK-NEXT:    [[EXITVAL_PH:%.*]] = phi i32 [ [[LOAD]], [[LOOP]] ], [ 0, [[LOOP_LATCH]] ]
+; CHECK-NEXT:    br label [[LOOP_EXIT]]
+; CHECK:       loop.exit:
+; CHECK-NEXT:    [[EXITVAL:%.*]] = phi i32 [ [[LOAD_PEEL]], [[LOOP_PEEL]] ], [ 0, [[LOOP_LATCH_PEEL]] ], [ [[EXITVAL_PH]], [[LOOP_EXIT_LOOPEXIT]] ]
+; CHECK-NEXT:    ret i32 [[EXITVAL]]
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi ptr [ %arg, %loop.latch ], [ null, %entry ]
+  %load = load i32, ptr null, align 4
+  br i1 false, label %loop.exit, label %loop.latch
+
+loop.latch:
+  br i1 false, label %loop.exit, label %loop
+
+loop.exit:
+  %exitval = phi i32 [ 0, %loop.latch ], [ %load, %loop ]
+  ret i32 %exitval
+}