https://github.com/el-ev updated
https://github.com/llvm/llvm-project/pull/135785
>From b5cac9cccc305a6af33bc0bc30d01965c5e7e333 Mon Sep 17 00:00:00 2001
From: Iris Shi <0...@owo.li>
Date: Tue, 15 Apr 2025 20:20:45 +0800
Subject: [PATCH] [ConstraintElim] Simplify `usub_with_overflow` when A uge B
---
.../Scalar/ConstraintElimination.cpp | 11 ++++
.../usub-with-overflow.ll | 54 +++++++++++--------
2 files changed, 44 insertions(+), 21 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index 15aba43721e57..71afd7a2203ef 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -1124,6 +1124,7 @@ void State::addInfoFor(BasicBlock &BB) {
// Enqueue overflow intrinsics for simplification.
case Intrinsic::sadd_with_overflow:
case Intrinsic::ssub_with_overflow:
+ case Intrinsic::usub_with_overflow:
case Intrinsic::ucmp:
case Intrinsic::scmp:
WorkList.push_back(
@@ -1765,6 +1766,16 @@ tryToSimplifyOverflowMath(IntrinsicInst *II,
ConstraintInfo &Info,
Changed = true;
break;
}
+ case Intrinsic::usub_with_overflow: {
+ // usub overflows iff A < B
+ // TODO: If the operation is guaranteed to overflow, we could
+ // also apply some simplifications.
+ if (DoesConditionHold(CmpInst::ICMP_UGE, A, B, Info)) {
+ replaceAddOrSubOverflowUses(II, A, B, ToRemove);
+ Changed = true;
+ }
+ break;
+ }
}
return Changed;
diff --git a/llvm/test/Transforms/ConstraintElimination/usub-with-overflow.ll
b/llvm/test/Transforms/ConstraintElimination/usub-with-overflow.ll
index 06bfd8269d97d..722116cc6ebd0 100644
--- a/llvm/test/Transforms/ConstraintElimination/usub-with-overflow.ll
+++ b/llvm/test/Transforms/ConstraintElimination/usub-with-overflow.ll
@@ -9,12 +9,14 @@ define i8 @usub_no_overflow_due_to_cmp_condition(i8 %a, i8
%b) {
; CHECK-NEXT: [[C_1:%.*]] = icmp uge i8 [[B:%.*]], [[A:%.*]]
; CHECK-NEXT: br i1 [[C_1]], label [[MATH:%.*]], label [[EXIT_FAIL:%.*]]
; CHECK: math:
-; CHECK-NEXT: [[OP:%.*]] = tail call { i8, i1 }
@llvm.usub.with.overflow.i8(i8 [[B]], i8 [[A]])
-; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[OP]], 1
+; CHECK-NEXT: [[RES:%.*]] = sub i8 [[B]], [[A]]
+; CHECK-NEXT: [[TMP1:%.*]] = insertvalue { i8, i1 } poison, i8 [[RES]], 0
+; CHECK-NEXT: [[TMP2:%.*]] = insertvalue { i8, i1 } [[TMP1]], i1 false, 1
+; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[TMP2]], 1
; CHECK-NEXT: br i1 [[STATUS]], label [[EXIT_FAIL]], label [[EXIT_OK:%.*]]
; CHECK: exit.ok:
-; CHECK-NEXT: [[RES:%.*]] = extractvalue { i8, i1 } [[OP]], 0
-; CHECK-NEXT: ret i8 [[RES]]
+; CHECK-NEXT: [[RES1:%.*]] = extractvalue { i8, i1 } [[TMP2]], 0
+; CHECK-NEXT: ret i8 [[RES1]]
; CHECK: exit.fail:
; CHECK-NEXT: ret i8 0
;
@@ -41,12 +43,14 @@ define i8 @usub_no_overflow_due_to_cmp_condition2(i8 %a, i8
%b) {
; CHECK-NEXT: [[C_1:%.*]] = icmp ule i8 [[B:%.*]], [[A:%.*]]
; CHECK-NEXT: br i1 [[C_1]], label [[EXIT_FAIL:%.*]], label [[MATH:%.*]]
; CHECK: math:
-; CHECK-NEXT: [[OP:%.*]] = tail call { i8, i1 }
@llvm.usub.with.overflow.i8(i8 [[B]], i8 [[A]])
-; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[OP]], 1
+; CHECK-NEXT: [[RES:%.*]] = sub i8 [[B]], [[A]]
+; CHECK-NEXT: [[TMP1:%.*]] = insertvalue { i8, i1 } poison, i8 [[RES]], 0
+; CHECK-NEXT: [[TMP2:%.*]] = insertvalue { i8, i1 } [[TMP1]], i1 false, 1
+; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[TMP2]], 1
; CHECK-NEXT: br i1 [[STATUS]], label [[EXIT_FAIL]], label [[EXIT_OK:%.*]]
; CHECK: exit.ok:
-; CHECK-NEXT: [[RES:%.*]] = extractvalue { i8, i1 } [[OP]], 0
-; CHECK-NEXT: ret i8 [[RES]]
+; CHECK-NEXT: [[RES1:%.*]] = extractvalue { i8, i1 } [[TMP2]], 0
+; CHECK-NEXT: ret i8 [[RES1]]
; CHECK: exit.fail:
; CHECK-NEXT: ret i8 0
;
@@ -75,13 +79,15 @@ define i8
@sub_no_overflow_due_to_cmp_condition_result_used(i8 %a, i8 %b) {
; CHECK-NEXT: [[C_1:%.*]] = icmp ule i8 [[B:%.*]], [[A:%.*]]
; CHECK-NEXT: br i1 [[C_1]], label [[EXIT_FAIL:%.*]], label [[MATH:%.*]]
; CHECK: math:
-; CHECK-NEXT: [[OP:%.*]] = tail call { i8, i1 }
@llvm.usub.with.overflow.i8(i8 [[B]], i8 [[A]])
+; CHECK-NEXT: [[RES:%.*]] = sub i8 [[B]], [[A]]
+; CHECK-NEXT: [[TMP1:%.*]] = insertvalue { i8, i1 } poison, i8 [[RES]], 0
+; CHECK-NEXT: [[OP:%.*]] = insertvalue { i8, i1 } [[TMP1]], i1 false, 1
; CHECK-NEXT: call void @use_res({ i8, i1 } [[OP]])
; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[OP]], 1
; CHECK-NEXT: br i1 [[STATUS]], label [[EXIT_FAIL]], label [[EXIT_OK:%.*]]
; CHECK: exit.ok:
-; CHECK-NEXT: [[RES:%.*]] = extractvalue { i8, i1 } [[OP]], 0
-; CHECK-NEXT: ret i8 [[RES]]
+; CHECK-NEXT: [[RES1:%.*]] = extractvalue { i8, i1 } [[OP]], 0
+; CHECK-NEXT: ret i8 [[RES1]]
; CHECK: exit.fail:
; CHECK-NEXT: ret i8 0
;
@@ -111,12 +117,14 @@ define i8 @usub_no_overflow_due_to_or_conds(i8 %a, i8 %b)
{
; CHECK-NEXT: [[OR:%.*]] = or i1 [[C_2]], [[C_1]]
; CHECK-NEXT: br i1 [[OR]], label [[EXIT_FAIL:%.*]], label [[MATH:%.*]]
; CHECK: math:
-; CHECK-NEXT: [[OP:%.*]] = tail call { i8, i1 }
@llvm.usub.with.overflow.i8(i8 [[B]], i8 [[A]])
-; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[OP]], 1
+; CHECK-NEXT: [[RES:%.*]] = sub i8 [[B]], [[A]]
+; CHECK-NEXT: [[TMP1:%.*]] = insertvalue { i8, i1 } poison, i8 [[RES]], 0
+; CHECK-NEXT: [[TMP2:%.*]] = insertvalue { i8, i1 } [[TMP1]], i1 false, 1
+; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[TMP2]], 1
; CHECK-NEXT: br i1 [[STATUS]], label [[EXIT_FAIL]], label [[EXIT_OK:%.*]]
; CHECK: exit.ok:
-; CHECK-NEXT: [[RES:%.*]] = extractvalue { i8, i1 } [[OP]], 0
-; CHECK-NEXT: ret i8 [[RES]]
+; CHECK-NEXT: [[RES1:%.*]] = extractvalue { i8, i1 } [[TMP2]], 0
+; CHECK-NEXT: ret i8 [[RES1]]
; CHECK: exit.fail:
; CHECK-NEXT: ret i8 0
;
@@ -147,8 +155,10 @@ define i8
@usub_no_overflow_due_to_or_conds_sub_result_not_used(i8 %a, i8 %b) {
; CHECK-NEXT: [[OR:%.*]] = or i1 [[C_2]], [[C_1]]
; CHECK-NEXT: br i1 [[OR]], label [[EXIT_FAIL:%.*]], label [[MATH:%.*]]
; CHECK: math:
-; CHECK-NEXT: [[OP:%.*]] = tail call { i8, i1 }
@llvm.usub.with.overflow.i8(i8 [[B]], i8 [[A]])
-; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[OP]], 1
+; CHECK-NEXT: [[TMP0:%.*]] = sub i8 [[B]], [[A]]
+; CHECK-NEXT: [[TMP1:%.*]] = insertvalue { i8, i1 } poison, i8 [[TMP0]], 0
+; CHECK-NEXT: [[TMP2:%.*]] = insertvalue { i8, i1 } [[TMP1]], i1 false, 1
+; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[TMP2]], 1
; CHECK-NEXT: br i1 [[STATUS]], label [[EXIT_FAIL]], label [[EXIT_OK:%.*]]
; CHECK: exit.ok:
; CHECK-NEXT: ret i8 20
@@ -181,12 +191,14 @@ define i8 @usub_no_overflow_due_to_and_conds(i8 %a, i8
%b) {
; CHECK-NEXT: [[AND:%.*]] = and i1 [[C_2]], [[C_1]]
; CHECK-NEXT: br i1 [[AND]], label [[MATH:%.*]], label [[EXIT_FAIL:%.*]]
; CHECK: math:
-; CHECK-NEXT: [[OP:%.*]] = tail call { i8, i1 }
@llvm.usub.with.overflow.i8(i8 [[B]], i8 [[A]])
-; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[OP]], 1
+; CHECK-NEXT: [[RES:%.*]] = sub i8 [[B]], [[A]]
+; CHECK-NEXT: [[TMP1:%.*]] = insertvalue { i8, i1 } poison, i8 [[RES]], 0
+; CHECK-NEXT: [[TMP2:%.*]] = insertvalue { i8, i1 } [[TMP1]], i1 false, 1
+; CHECK-NEXT: [[STATUS:%.*]] = extractvalue { i8, i1 } [[TMP2]], 1
; CHECK-NEXT: br i1 [[STATUS]], label [[EXIT_FAIL]], label [[EXIT_OK:%.*]]
; CHECK: exit.ok:
-; CHECK-NEXT: [[RES:%.*]] = extractvalue { i8, i1 } [[OP]], 0
-; CHECK-NEXT: ret i8 [[RES]]
+; CHECK-NEXT: [[RES1:%.*]] = extractvalue { i8, i1 } [[TMP2]], 0
+; CHECK-NEXT: ret i8 [[RES1]]
; CHECK: exit.fail:
; CHECK-NEXT: ret i8 0
;
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