[llvm] 77dd579 - [SCEV] Remove incorrect assert

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2021-11-29T17:09:12+01:00
New Revision: 77dd579827f2e7574be4bbf3f94a48930e7b094f

URL: https://github.com/llvm/llvm-project/commit/77dd579827f2e7574be4bbf3f94a48930e7b094f
DIFF: https://github.com/llvm/llvm-project/commit/77dd579827f2e7574be4bbf3f94a48930e7b094f.diff

LOG: [SCEV] Remove incorrect assert

Fix assertion failure reported on D113349 by removing the assert.
While the produced expression should be equivalent, it may not
be strictly the same, e.g. due to lazy nowrap flag updates. Similar
to what the main createSCEV() code does, simply retain the old
value map entry if one already exists.

Added: 
    llvm/test/Analysis/ScalarEvolution/addrec-computed-during-addrec-calculation.ll

Modified: 
    llvm/lib/Analysis/ScalarEvolution.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 8007cefc4bd79..d1e2e3486a675 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4095,14 +4095,13 @@ void ScalarEvolution::eraseValueFromMap(Value *V) {
 }
 
 void ScalarEvolution::insertValueToMap(Value *V, const SCEV *S) {
+  // A recursive query may have already computed the SCEV. It should be
+  // equivalent, but may not necessarily be exactly the same, e.g. due to lazily
+  // inferred nowrap flags.
   auto It = ValueExprMap.find_as(V);
   if (It == ValueExprMap.end()) {
     ValueExprMap.insert({SCEVCallbackVH(V, this), S});
     ExprValueMap[S].insert({V, nullptr});
-  } else {
-    // A recursive query may have already computed the SCEV. It should have
-    // arrived at the same value.
-    assert(It->second == S);
   }
 }
 

diff  --git a/llvm/test/Analysis/ScalarEvolution/addrec-computed-during-addrec-calculation.ll b/llvm/test/Analysis/ScalarEvolution/addrec-computed-during-addrec-calculation.ll
new file mode 100644
index 0000000000000..f0ee06e9072fd
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/addrec-computed-during-addrec-calculation.ll
@@ -0,0 +1,67 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt -disable-output "-passes=print<scalar-evolution>" < %s 2>&1 | FileCheck %s
+
+; In this case the %iv2 addrec is calculated and added to the value map in a
+; recursive call trying to calculate that same addrec. Due to lazy nowrap flag
+; inference, the exact SCEV calculated both times ends up being 
diff erent,
+; though both expressions are correct. Make sure we don't assert in this case.
+
+define void @test(i32* %p) {
+; CHECK-LABEL: 'test'
+; CHECK-NEXT:  Classifying expressions for: @test
+; CHECK-NEXT:    %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop.latch ]
+; CHECK-NEXT:    --> %iv U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop.header: Variant, %loop2: Invariant, %loop3: Invariant }
+; CHECK-NEXT:    %iv2 = phi i32 [ %iv, %loop.header ], [ %iv2.next, %loop2 ]
+; CHECK-NEXT:    --> {%iv,+,1}<nsw><%loop2> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop2: Computable, %loop.header: Variant }
+; CHECK-NEXT:    %iv2.next = add i32 %iv2, 1
+; CHECK-NEXT:    --> {(1 + %iv),+,1}<nw><%loop2> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop2: Computable, %loop.header: Variant }
+; CHECK-NEXT:    %v = load i32, i32* %p, align 4
+; CHECK-NEXT:    --> %v U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop2: Variant, %loop.header: Variant }
+; CHECK-NEXT:    %iv2.ext = sext i32 %iv2 to i64
+; CHECK-NEXT:    --> (sext i32 {%iv,+,1}<nsw><%loop2> to i64) U: [-2147483648,2147483648) S: [-2147483648,2147483648) Exits: <<Unknown>> LoopDispositions: { %loop.header: Variant, %loop2: Computable, %loop3: Invariant }
+; CHECK-NEXT:    %iv3 = phi i64 [ %iv2.ext, %loop2.end ], [ %iv3.next, %loop3 ]
+; CHECK-NEXT:    --> {(sext i32 {%iv,+,1}<nsw><%loop2> to i64),+,1}<nsw><%loop3> U: [-2147483648,2147483648) S: [-2147483648,2147483648) Exits: (sext i32 {%iv,+,1}<nsw><%loop2> to i64) LoopDispositions: { %loop3: Computable, %loop.header: Variant }
+; CHECK-NEXT:    %iv3.next = add nsw i64 %iv3, 1
+; CHECK-NEXT:    --> {(1 + (sext i32 {%iv,+,1}<nsw><%loop2> to i64))<nsw>,+,1}<nsw><%loop3> U: [-2147483647,2147483649) S: [-2147483647,2147483649) Exits: (1 + (sext i32 {%iv,+,1}<nsw><%loop2> to i64))<nsw> LoopDispositions: { %loop3: Computable, %loop.header: Variant }
+; CHECK-NEXT:    %iv.next = trunc i64 %iv3 to i32
+; CHECK-NEXT:    --> {{\{}}{%iv,+,1}<nsw><%loop2>,+,1}<%loop3> U: full-set S: full-set --> {%iv,+,1}<nsw><%loop2> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop.header: Variant, %loop2: Variant, %loop3: Computable }
+; CHECK-NEXT:  Determining loop execution counts for: @test
+; CHECK-NEXT:  Loop %loop2: Unpredictable backedge-taken count.
+; CHECK-NEXT:  Loop %loop2: max backedge-taken count is -1
+; CHECK-NEXT:  Loop %loop2: Unpredictable predicated backedge-taken count.
+; CHECK-NEXT:  Loop %loop3: backedge-taken count is false
+; CHECK-NEXT:  Loop %loop3: max backedge-taken count is false
+; CHECK-NEXT:  Loop %loop3: Predicated backedge-taken count is false
+; CHECK-NEXT:   Predicates:
+; CHECK:       Loop %loop3: Trip multiple is 1
+; CHECK-NEXT:  Loop %loop.header: <multiple exits> Unpredictable backedge-taken count.
+; CHECK-NEXT:  Loop %loop.header: Unpredictable max backedge-taken count.
+; CHECK-NEXT:  Loop %loop.header: Unpredictable predicated backedge-taken count.
+;
+entry:
+  br label %loop.header
+
+loop.header:
+  %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop.latch ]
+  br label %loop2
+
+loop2:
+  %iv2 = phi i32 [ %iv, %loop.header ], [ %iv2.next, %loop2 ]
+  %iv2.next = add i32 %iv2, 1
+  %v = load i32, i32* %p
+  %cmp = icmp slt i32 %iv2, %v
+  br i1 %cmp, label %loop2, label %loop2.end
+
+loop2.end:
+  %iv2.ext = sext i32 %iv2 to i64
+  br label %loop3
+
+loop3:
+  %iv3 = phi i64 [ %iv2.ext, %loop2.end ], [ %iv3.next, %loop3 ]
+  %iv3.next = add nsw i64 %iv3, 1
+  br i1 false, label %loop3, label %loop.latch
+
+loop.latch:
+  %iv.next = trunc i64 %iv3 to i32
+  br label %loop.header
+}