[PATCH] D73181: [SCEV] Do not use backedge SCEV of PHI if its input is another PHI

[Denis Antrushin via Phabricator via llvm-commits]

dantrushin updated this revision to Diff 239813.
dantrushin added a comment.

- Check that PHI's input is the PHI from the same block(loop);
- Add comment to test explaining its complexity


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D73181/new/

https://reviews.llvm.org/D73181

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/pr44605.ll


Index: llvm/test/Analysis/ScalarEvolution/pr44605.ll
===================================================================
--- /dev/null
+++ llvm/test/Analysis/ScalarEvolution/pr44605.ll
@@ -0,0 +1,67 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; NOTE: Only %local_6_6 and %local_3_4 nodes are important here.
+;       All other instructions are needed to lure LLVM into executing
+;       specific code to trigger a bug.
+; RUN: opt < %s -indvars -S | FileCheck %s
+define i32 @test() {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[OUTER:%.*]]
+; CHECK:       outer:
+; CHECK-NEXT:    [[LOCAL_6_6:%.*]] = phi i32 [ 10, [[ENTRY:%.*]] ], [ [[TMP5:%.*]], [[LATCH:%.*]] ]
+; CHECK-NEXT:    [[LOCAL_4_5:%.*]] = phi i32 [ 56587, [[ENTRY]] ], [ 0, [[LATCH]] ]
+; CHECK-NEXT:    [[LOCAL_3_4:%.*]] = phi i32 [ 2, [[ENTRY]] ], [ [[LOCAL_6_6]], [[LATCH]] ]
+; CHECK-NEXT:    [[DOTUDIV:%.*]] = udiv i32 [[LOCAL_6_6]], 8361
+; CHECK-NEXT:    br label [[INNER:%.*]]
+; CHECK:       inner:
+; CHECK-NEXT:    [[LOCAL_7_3:%.*]] = phi i32 [ 2, [[OUTER]] ], [ [[TMP3:%.*]], [[INNER]] ]
+; CHECK-NEXT:    [[LOCAL_4_5_PN:%.*]] = phi i32 [ [[LOCAL_4_5]], [[OUTER]] ], [ [[TMP2:%.*]], [[INNER]] ]
+; CHECK-NEXT:    [[LOCAL_3_31:%.*]] = mul i32 [[LOCAL_4_5_PN]], [[DOTUDIV]]
+; CHECK-NEXT:    [[TMP0:%.*]] = mul nuw nsw i32 [[LOCAL_7_3]], [[DOTUDIV]]
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i32 [[TMP0]], [[LOCAL_3_4]]
+; CHECK-NEXT:    [[TMP2]] = add i32 [[TMP1]], [[LOCAL_3_31]]
+; CHECK-NEXT:    [[TMP3]] = add nuw nsw i32 [[LOCAL_7_3]], 1
+; CHECK-NEXT:    [[TMP4:%.*]] = icmp ugt i32 [[LOCAL_7_3]], 4
+; CHECK-NEXT:    br i1 [[TMP4]], label [[LATCH]], label [[INNER]]
+; CHECK:       latch:
+; CHECK-NEXT:    [[DOTLCSSA:%.*]] = phi i32 [ [[TMP2]], [[INNER]] ]
+; CHECK-NEXT:    [[TMP5]] = add nuw nsw i32 [[LOCAL_6_6]], 1
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp ugt i32 [[LOCAL_6_6]], 276
+; CHECK-NEXT:    br i1 [[TMP6]], label [[RETURN:%.*]], label [[OUTER]]
+; CHECK:       return:
+; CHECK-NEXT:    [[DOTLCSSA_LCSSA:%.*]] = phi i32 [ [[DOTLCSSA]], [[LATCH]] ]
+; CHECK-NEXT:    ret i32 [[DOTLCSSA_LCSSA]]
+;
+entry:
+  br label %outer
+
+outer:
+  %local_6_6 = phi i32 [ 10, %entry ], [ %5, %latch ]
+  %local_4_5 = phi i32 [ 56587, %entry ], [ 0, %latch ]
+  %local_3_4 = phi i32 [ 2, %entry ], [ %local_6_6, %latch ]
+  %.udiv = udiv i32 %local_6_6, 8361
+  br label %inner
+
+inner:
+  %local_7_3 = phi i32 [ 2, %outer ], [ %3, %inner ]
+  %local_4_5.pn = phi i32 [ %local_4_5, %outer ], [ %2, %inner ]
+  %local_3_31 = mul i32 %local_4_5.pn, %.udiv
+  %0 = mul i32 %local_7_3, %.udiv
+  %1 = sub i32 %0, %local_3_4
+  %2 = add i32 %1, %local_3_31
+  %3 = add nuw nsw i32 %local_7_3, 1
+  %4 = icmp ugt i32 %local_7_3, 4
+  br i1 %4, label %latch, label %inner
+
+latch:
+  %.lcssa = phi i32 [ %2, %inner ]
+  %5 = add nuw nsw i32 %local_6_6, 1
+  %6 = icmp ugt i32 %local_6_6, 276
+  br i1 %6, label %return, label %outer
+
+return:
+  %.lcssa.lcssa = phi i32 [ %.lcssa, %latch ]
+  ret i32 %.lcssa.lcssa
+
+}
+
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -8235,14 +8235,18 @@
             if (!MultipleInitValues && InitValue)
               return getSCEV(InitValue);
           }
-          // Do we have a loop invariant value flowing around the backedge
+          // Do we have a PHI value we can materialize
           // for a loop which must execute the backedge?
           if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) &&
               isKnownPositive(BackedgeTakenCount) &&
               PN->getNumIncomingValues() == 2) {
             unsigned InLoopPred = LI->contains(PN->getIncomingBlock(0)) ? 0 : 1;
-            const SCEV *OnBackedge = getSCEV(PN->getIncomingValue(InLoopPred));
-            if (IsAvailableOnEntry(LI, DT, OnBackedge, PN->getParent()))
+            BasicBlock *Header = PN->getParent();
+            Value *BackedgeVal = PN->getIncomingValue(InLoopPred);
+            const SCEV *OnBackedge = getSCEV(BackedgeVal);
+            if (!(isa<PHINode>(BackedgeVal) &&
+                  cast<PHINode>(BackedgeVal)->getParent() == Header) &&
+                IsAvailableOnEntry(LI, DT, OnBackedge, Header))
               return OnBackedge;
           }
           if (auto *BTCC = dyn_cast<SCEVConstant>(BackedgeTakenCount)) {


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