[PATCH] D59617: [ValueTracking] Use ConstantRange based overflow check for signed sub

[Nikita Popov via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL356685: [ValueTracking] Use ConstantRange based overflow check for signed sub (authored by nikic, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D59617?vs=191589&id=191735#toc

Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D59617/new/

https://reviews.llvm.org/D59617

Files:
  llvm/trunk/lib/Analysis/ValueTracking.cpp
  llvm/trunk/test/Transforms/InstCombine/sub.ll


Index: llvm/trunk/test/Transforms/InstCombine/sub.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/sub.ll
+++ llvm/trunk/test/Transforms/InstCombine/sub.ll
@@ -1271,7 +1271,7 @@
 ; CHECK-LABEL: @nsw_inference1(
 ; CHECK-NEXT:    [[X2:%.*]] = or i32 [[X:%.*]], 1024
 ; CHECK-NEXT:    [[Y2:%.*]] = and i32 [[Y:%.*]], 1
-; CHECK-NEXT:    [[Z:%.*]] = sub nuw i32 [[X2]], [[Y2]]
+; CHECK-NEXT:    [[Z:%.*]] = sub nuw nsw i32 [[X2]], [[Y2]]
 ; CHECK-NEXT:    ret i32 [[Z]]
 ;
   %x2 = or i32 %x, 1024
@@ -1284,7 +1284,7 @@
 ; CHECK-LABEL: @nsw_inference2(
 ; CHECK-NEXT:    [[X2:%.*]] = and i32 [[X:%.*]], -1025
 ; CHECK-NEXT:    [[Y2:%.*]] = or i32 [[Y:%.*]], -2
-; CHECK-NEXT:    [[Z:%.*]] = sub i32 [[X2]], [[Y2]]
+; CHECK-NEXT:    [[Z:%.*]] = sub nsw i32 [[X2]], [[Y2]]
 ; CHECK-NEXT:    ret i32 [[Z]]
 ;
   %x2 = and i32 %x, -1025
Index: llvm/trunk/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp
@@ -4190,17 +4190,12 @@
     return OverflowResult::NeverOverflows;
 
   KnownBits LHSKnown = computeKnownBits(LHS, DL, 0, AC, CxtI, DT);
-
   KnownBits RHSKnown = computeKnownBits(RHS, DL, 0, AC, CxtI, DT);
-
-  // Subtraction of two 2's complement numbers having identical signs will
-  // never overflow.
-  if ((LHSKnown.isNegative() && RHSKnown.isNegative()) ||
-      (LHSKnown.isNonNegative() && RHSKnown.isNonNegative()))
-    return OverflowResult::NeverOverflows;
-
-  // TODO: implement logic similar to checkRippleForAdd
-  return OverflowResult::MayOverflow;
+  ConstantRange LHSRange =
+      ConstantRange::fromKnownBits(LHSKnown, /*signed*/ true);
+  ConstantRange RHSRange =
+      ConstantRange::fromKnownBits(RHSKnown, /*signed*/ true);
+  return mapOverflowResult(LHSRange.signedSubMayOverflow(RHSRange));
 }
 
 bool llvm::isOverflowIntrinsicNoWrap(const IntrinsicInst *II,


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