[PATCH] D60469: [ValueTracking] Use computeConstantRange() for signed sub overflow determination

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: lebedev.ri, spatel.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

Followup to D60420 <https://reviews.llvm.org/D60420> for the signed subtraction case.


Repository:
  rL LLVM

https://reviews.llvm.org/D60469

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstCombine/saturating-add-sub.ll
  llvm/test/Transforms/InstCombine/ssub-with-overflow.ll


Index: llvm/test/Transforms/InstCombine/ssub-with-overflow.ll
===================================================================
--- llvm/test/Transforms/InstCombine/ssub-with-overflow.ll
+++ llvm/test/Transforms/InstCombine/ssub-with-overflow.ll
@@ -22,9 +22,9 @@
 
 define { i32, i1 } @fold_mixed_signs(i32 %x) {
 ; CHECK-LABEL: @fold_mixed_signs(
-; CHECK-NEXT:    [[A:%.*]] = add nsw i32 [[X:%.*]], -13
-; CHECK-NEXT:    [[B:%.*]] = tail call { i32, i1 } @llvm.ssub.with.overflow.i32(i32 [[A]], i32 -7)
-; CHECK-NEXT:    ret { i32, i1 } [[B]]
+; CHECK-NEXT:    [[B:%.*]] = add nsw i32 [[X:%.*]], -6
+; CHECK-NEXT:    [[TMP1:%.*]] = insertvalue { i32, i1 } { i32 undef, i1 false }, i32 [[B]], 0
+; CHECK-NEXT:    ret { i32, i1 } [[TMP1]]
 ;
   %a = sub nsw i32 %x, 13
   %b = tail call { i32, i1 } @llvm.ssub.with.overflow.i32(i32 %a, i32 -7)
Index: llvm/test/Transforms/InstCombine/saturating-add-sub.ll
===================================================================
--- llvm/test/Transforms/InstCombine/saturating-add-sub.ll
+++ llvm/test/Transforms/InstCombine/saturating-add-sub.ll
@@ -928,7 +928,7 @@
 ; CHECK-LABEL: @test_scalar_ssub_add_nsw_no_ov(
 ; CHECK-NEXT:    [[AA:%.*]] = add nsw i8 [[A:%.*]], 7
 ; CHECK-NEXT:    [[BB:%.*]] = and i8 [[B:%.*]], 7
-; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.ssub.sat.i8(i8 [[AA]], i8 [[BB]])
+; CHECK-NEXT:    [[R:%.*]] = sub nsw i8 [[AA]], [[BB]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %aa = add nsw i8 %a, 7
@@ -954,7 +954,7 @@
 ; CHECK-LABEL: @test_vector_ssub_add_nsw_no_ov_splat(
 ; CHECK-NEXT:    [[AA:%.*]] = add nsw <2 x i8> [[A:%.*]], <i8 7, i8 7>
 ; CHECK-NEXT:    [[BB:%.*]] = and <2 x i8> [[B:%.*]], <i8 7, i8 7>
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i8> @llvm.ssub.sat.v2i8(<2 x i8> [[AA]], <2 x i8> [[BB]])
+; CHECK-NEXT:    [[R:%.*]] = sub nsw <2 x i8> [[AA]], [[BB]]
 ; CHECK-NEXT:    ret <2 x i8> [[R]]
 ;
   %aa = add nsw <2 x i8> %a, <i8 7, i8 7>
@@ -967,7 +967,7 @@
 ; CHECK-LABEL: @test_vector_ssub_add_nsw_no_ov_nonsplat1(
 ; CHECK-NEXT:    [[AA:%.*]] = add nsw <2 x i8> [[A:%.*]], <i8 7, i8 7>
 ; CHECK-NEXT:    [[BB:%.*]] = and <2 x i8> [[B:%.*]], <i8 7, i8 6>
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i8> @llvm.ssub.sat.v2i8(<2 x i8> [[AA]], <2 x i8> [[BB]])
+; CHECK-NEXT:    [[R:%.*]] = sub nsw <2 x i8> [[AA]], [[BB]]
 ; CHECK-NEXT:    ret <2 x i8> [[R]]
 ;
   %aa = add nsw <2 x i8> %a, <i8 7, i8 7>
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -4192,12 +4192,10 @@
       ComputeNumSignBits(RHS, DL, 0, AC, CxtI, DT) > 1)
     return OverflowResult::NeverOverflows;
 
-  KnownBits LHSKnown = computeKnownBits(LHS, DL, 0, AC, CxtI, DT);
-  KnownBits RHSKnown = computeKnownBits(RHS, DL, 0, AC, CxtI, DT);
-  ConstantRange LHSRange =
-      ConstantRange::fromKnownBits(LHSKnown, /*signed*/ true);
-  ConstantRange RHSRange =
-      ConstantRange::fromKnownBits(RHSKnown, /*signed*/ true);
+  ConstantRange LHSRange = computeConstantRangeIncludingKnownBits(
+      LHS, /*ForSigned=*/true, DL, /*Depth=*/0, AC, CxtI, DT);
+  ConstantRange RHSRange = computeConstantRangeIncludingKnownBits(
+      RHS, /*ForSigned=*/true, DL, /*Depth=*/0, AC, CxtI, DT);
   return mapOverflowResult(LHSRange.signedSubMayOverflow(RHSRange));
 }
 


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