[PATCH] D148084: [SCEV] Preserve NSW for AddRec multiplied by -1 if it cannot be signed minimum

[Dmitry Makogon via Phabricator via llvm-commits]

dmakogon updated this revision to Diff 512759.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D148084/new/

https://reviews.llvm.org/D148084

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/decrementing_addrecs.ll
  llvm/test/Analysis/ScalarEvolution/different-loops-recs.ll
  llvm/test/Analysis/ScalarEvolution/sext-iv-2.ll


Index: llvm/test/Analysis/ScalarEvolution/sext-iv-2.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/sext-iv-2.ll
+++ llvm/test/Analysis/ScalarEvolution/sext-iv-2.ll
@@ -3,7 +3,7 @@
 ; CHECK: %tmp3 = sext i8 %tmp2 to i32
 ; CHECK: -->  (sext i8 {0,+,1}<%bb1> to i32) U: [-128,128) S: [-128,128)               Exits: -1
 ; CHECK: %tmp4 = mul i32 %tmp3, %i.02
-; CHECK: -->  ((sext i8 {0,+,1}<%bb1> to i32) * {0,+,1}<nuw><nsw><%bb>) U: [-3968,3938) S: [-3968,3938)                Exits: {0,+,-1}<nw><%bb>
+; CHECK: -->  ((sext i8 {0,+,1}<%bb1> to i32) * {0,+,1}<nuw><nsw><%bb>) U: [-3968,3938) S: [-3968,3938)                Exits: {0,+,-1}<nsw><%bb>
 
 ; These sexts are not foldable.
 
Index: llvm/test/Analysis/ScalarEvolution/different-loops-recs.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/different-loops-recs.ll
+++ llvm/test/Analysis/ScalarEvolution/different-loops-recs.ll
@@ -275,7 +275,7 @@
 ; CHECK:       %tmp9 = sext i8 %tmp8 to i64
 ; CHECK-NEXT:  -->  (sext i8 %tmp8 to i64) U: [-128,128) S: [-128,128)
 ; CHECK:       %tmp10 = sub i64 %tmp9, %tmp7
-; CHECK-NEXT:  -->  ((sext i8 %tmp8 to i64) + {-2,+,-1}<nw><%loop2>) U: [9223372036854775682,126) S: [9223372036854775682,126)
+; CHECK-NEXT:  -->  ((sext i8 %tmp8 to i64) + {-2,+,-1}<nsw><%loop2>) U: [9223372036854775682,126) S: [9223372036854775682,126)
 ; CHECK:       %tmp11 = add i64 %tmp10, undef
 ; CHECK-NEXT:  -->  ((sext i8 %tmp8 to i64) + {(-2 + undef),+,-1}<nw><%loop2>)
 ; CHECK:       %tmp13 = trunc i64 %tmp11 to i32
Index: llvm/test/Analysis/ScalarEvolution/decrementing_addrecs.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/decrementing_addrecs.ll
+++ llvm/test/Analysis/ScalarEvolution/decrementing_addrecs.ll
@@ -40,7 +40,7 @@
 ; DEFAULT-NEXT:    %b = sub i32 %n.minus.1, %i
 ; DEFAULT-NEXT:    --> {(-1 + %n),+,-1}<nsw><%loop> U: full-set S: full-set Exits: 0 LoopDispositions: { %loop: Computable }
 ; DEFAULT-NEXT:    %c = sub i32 2147483647, %i
-; DEFAULT-NEXT:    --> {2147483647,+,-1}<nw><%loop> U: [1,-2147483648) S: [1,-2147483648) Exits: (-2147483648 + (-1 * %n)) LoopDispositions: { %loop: Computable }
+; DEFAULT-NEXT:    --> {2147483647,+,-1}<nsw><%loop> U: [1,-2147483648) S: [1,-2147483648) Exits: (-2147483648 + (-1 * %n)) LoopDispositions: { %loop: Computable }
 ; DEFAULT-NEXT:    %i.next = add nuw nsw i32 %i, 1
 ; DEFAULT-NEXT:    --> {1,+,1}<nuw><nsw><%loop> U: [1,-2147483648) S: [1,-2147483648) Exits: %n LoopDispositions: { %loop: Computable }
 ; DEFAULT-NEXT:    %j.next = add nsw i32 %j, -1
@@ -66,7 +66,7 @@
 ; EXPENSIVE_SHARPENING-NEXT:    %b = sub i32 %n.minus.1, %i
 ; EXPENSIVE_SHARPENING-NEXT:    --> {(-1 + %n),+,-1}<nsw><%loop> U: [0,2147483647) S: [0,2147483647) Exits: 0 LoopDispositions: { %loop: Computable }
 ; EXPENSIVE_SHARPENING-NEXT:    %c = sub i32 2147483647, %i
-; EXPENSIVE_SHARPENING-NEXT:    --> {2147483647,+,-1}<nw><%loop> U: [1,-2147483648) S: [1,-2147483648) Exits: (-2147483648 + (-1 * %n)) LoopDispositions: { %loop: Computable }
+; EXPENSIVE_SHARPENING-NEXT:    --> {2147483647,+,-1}<nsw><%loop> U: [1,-2147483648) S: [1,-2147483648) Exits: (-2147483648 + (-1 * %n)) LoopDispositions: { %loop: Computable }
 ; EXPENSIVE_SHARPENING-NEXT:    %i.next = add nuw nsw i32 %i, 1
 ; EXPENSIVE_SHARPENING-NEXT:    --> {1,+,1}<nuw><nsw><%loop> U: [1,-2147483648) S: [1,-2147483648) Exits: %n LoopDispositions: { %loop: Computable }
 ; EXPENSIVE_SHARPENING-NEXT:    %j.next = add nsw i32 %j, -1
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3192,9 +3192,18 @@
           for (const SCEV *AddRecOp : AddRec->operands())
             Operands.push_back(getMulExpr(Ops[0], AddRecOp, SCEV::FlagAnyWrap,
                                           Depth + 1));
-
+          // Let M be the minimum representable signed value. AddRec with nsw
+          // multiplied by -1 can have signed overflow if and only if it takes a
+          // value of M: M * (-1) would stay M and (M + 1) * (-1) would be the
+          // maximum signed value. In all other cases signed overflow is
+          // impossible.
+          auto FlagsMask = SCEV::FlagNW;
+          auto MinInt =
+              APInt::getSignedMinValue(getTypeSizeInBits(AddRec->getType()));
+          if (getSignedRangeMin(AddRec) != MinInt)
+            FlagsMask = setFlags(FlagsMask, SCEV::FlagNSW);
           return getAddRecExpr(Operands, AddRec->getLoop(),
-                               AddRec->getNoWrapFlags(SCEV::FlagNW));
+                               AddRec->getNoWrapFlags(FlagsMask));
         }
       }
     }


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D148084.512759.patch
Type: text/x-patch
Size: 4857 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20230412/af677fe1/attachment.bin>