[PATCH] D134739: [SCEVExpander] Check expr is available for traversed InsterPts.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: reames, spatel, efriedma.
Herald added subscribers: javed.absar, hiraditya.
Herald added a project: All.
fhahn requested review of this revision.
Herald added a project: LLVM.

Update SCEVExpander::expand() to check if the current expression is
available for for different insert points the loop traverses.

This ensures that existing values for LCSSA phis can be re-used; their
insert point will always be in a loop exit block, even if the expression
allows hoisting in earlier blocks.

Alternative to D132704 <https://reviews.llvm.org/D132704>.

Fixes #57000.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D134739

Files:
  llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
  llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll


Index: llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll
===================================================================
--- llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll
+++ llvm/test/Transforms/IndVarSimplify/lcssa-preservation.ll
@@ -86,3 +86,59 @@
   %res.lcssa2 = phi i64 [ %res.lcssa, %loop1.latch ]
   ret i64 %res.lcssa2
 }
+
+; Check that it does not crash because the incoming values of an LCSSA phi are
+; equal.
+define void @pr57000(i64 %a) {
+; CHECK-LABEL: @pr57000(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP_1_OUTER:%.*]]
+; CHECK:       loop.1.loopexit:
+; CHECK-NEXT:    br label [[LOOP_1_OUTER]]
+; CHECK:       loop.1.outer:
+; CHECK-NEXT:    br label [[LOOP_1:%.*]]
+; CHECK:       loop.1:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sle i64 [[A:%.*]], 2546175499358690212
+; CHECK-NEXT:    [[CMP_EXT:%.*]] = zext i1 [[CMP]] to i8
+; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP_1]], label [[LOOP_2_HEADER_PREHEADER:%.*]]
+; CHECK:       loop.2.header.preheader:
+; CHECK-NEXT:    [[CMP_LCSSA:%.*]] = phi i1 [ [[CMP]], [[LOOP_1]] ]
+; CHECK-NEXT:    [[CMP_EXT_LCSSA:%.*]] = phi i8 [ [[CMP_EXT]], [[LOOP_1]] ]
+; CHECK-NEXT:    br label [[LOOP_2_HEADER_OUTER:%.*]]
+; CHECK:       loop.2.header.outer:
+; CHECK-NEXT:    br label [[LOOP_2_HEADER:%.*]]
+; CHECK:       loop.2.header:
+; CHECK-NEXT:    switch i8 [[CMP_EXT_LCSSA]], label [[LOOP_1_LOOPEXIT:%.*]] [
+; CHECK-NEXT:    i8 -1, label [[LOOP_2_LATCH:%.*]]
+; CHECK-NEXT:    i8 1, label [[LOOP_2_LATCH]]
+; CHECK-NEXT:    i8 4, label [[LOOP_2_HEADER]]
+; CHECK-NEXT:    ]
+; CHECK:       loop.2.latch:
+; CHECK-NEXT:    [[CMP_TRUNC_LCSSA1:%.*]] = phi i1 [ [[CMP_LCSSA]], [[LOOP_2_HEADER]] ], [ [[CMP_LCSSA]], [[LOOP_2_HEADER]] ]
+; CHECK-NEXT:    call void @use(i1 [[CMP_TRUNC_LCSSA1]])
+; CHECK-NEXT:    br label [[LOOP_2_HEADER_OUTER]]
+;
+entry:
+  br label %loop.1
+
+loop.1:
+  %p.1 = phi i1 [ 0 , %entry ], [ %p.1, %loop.1 ], [ %p.2, %loop.2.header ]
+  %cmp = icmp sle i64 %a, 2546175499358690212
+  %cmp.ext = zext i1 %cmp to i8
+  br i1 %cmp, label %loop.1, label %loop.2.header
+
+loop.2.header:
+  %p.2 = phi i1 [ %p.1, %loop.1 ], [ %p.2, %loop.2.header ], [ %cmp, %loop.2.latch ]
+  %cmp.trunc = trunc i8 %cmp.ext to i1
+  switch i8 %cmp.ext, label %loop.1 [
+  i8 -1, label %loop.2.latch
+  i8 1, label %loop.2.latch
+  i8 4, label %loop.2.header
+  ]
+
+loop.2.latch:
+  call void @use(i1 %cmp.trunc)
+  br label %loop.2.header
+}
+
+declare void @use(i1)
Index: llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
===================================================================
--- llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -1838,6 +1838,11 @@
   if (SafeToHoist(S)) {
     for (Loop *L = SE.LI.getLoopFor(Builder.GetInsertBlock());;
          L = L->getParentLoop()) {
+      // Check to see if we already expanded this here.
+      auto I = InsertedExpressions.find(std::make_pair(S, InsertPt));
+      if (I != InsertedExpressions.end())
+        return I->second;
+
       if (SE.isLoopInvariant(S, L)) {
         if (!L) break;
         if (BasicBlock *Preheader = L->getLoopPreheader())


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