[llvm] [InstCombine] Fold usub_sat((sub nuw C1, A), C2) to usub_sat(C1 - C2, A) or 0 (PR #82280)
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Mon Feb 19 13:43:15 PST 2024
https://github.com/elhewaty created https://github.com/llvm/llvm-project/pull/82280
- [InstCombine] Add test coverage for folding usub_sat((sub nuw C1, A), C2) to usub_sat(C1 - C2, A) or 0(NFC)
- [InstCombine] Fold usub_sat((sub nuw C1, A), C2) to usub_sat(C1 - C2, A) or 0
- Fixes: https://github.com/llvm/llvm-project/issues/82177
- Alive2: https://alive2.llvm.org/ce/z/4w-77P
>From 4ed5704bf153ccf2732038d17b1dca24266e6c72 Mon Sep 17 00:00:00 2001
From: Mohamed Atef <mohamedatef1698 at gmail.com>
Date: Mon, 19 Feb 2024 22:15:10 +0200
Subject: [PATCH 1/2] [InstCombine] Add test coverage for folding usub_sat((sub
nuw C1, A), C2) to usub_sat(C1 - C2, A) or 0(NFC)
---
.../InstCombine/unsigned_saturated_sub.ll | 76 +++++++++++++++++++
1 file changed, 76 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/unsigned_saturated_sub.ll b/llvm/test/Transforms/InstCombine/unsigned_saturated_sub.ll
index 5cece931b8d987..edf7c70b3c8a1a 100644
--- a/llvm/test/Transforms/InstCombine/unsigned_saturated_sub.ll
+++ b/llvm/test/Transforms/InstCombine/unsigned_saturated_sub.ll
@@ -7,6 +7,82 @@
declare void @use(i64)
declare void @usei32(i32)
declare void @usei1(i1)
+declare i32 @llvm.usub.sat.i32(i32, i32)
+declare i16 @llvm.usub.sat.i16(i16, i16)
+
+; usub_sat((sub nuw C1, A), C2) to usub_sat(C1 - C2, A) or 0
+
+define i32 @usub_sat_C1_C2(i32 %a){
+; CHECK-LABEL: @usub_sat_C1_C2(
+; CHECK-NEXT: [[ADD:%.*]] = sub nuw i32 64, [[A:%.*]]
+; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[ADD]], i32 14)
+; CHECK-NEXT: ret i32 [[COND]]
+;
+ %add = sub nuw i32 64, %a
+ %cond = call i32 @llvm.usub.sat.i32(i32 %add, i32 14)
+ ret i32 %cond
+}
+
+define i32 @usub_sat_C1_C2_produce_0(i32 %a){
+; CHECK-LABEL: @usub_sat_C1_C2_produce_0(
+; CHECK-NEXT: [[ADD:%.*]] = sub nuw i32 14, [[A:%.*]]
+; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[ADD]], i32 14)
+; CHECK-NEXT: ret i32 [[COND]]
+;
+ %add = sub nuw i32 14, %a
+ %cond = call i32 @llvm.usub.sat.i32(i32 %add, i32 14)
+ ret i32 %cond
+}
+
+define i32 @usub_sat_C1_C2_produce_0_too(i32 %a){
+; CHECK-LABEL: @usub_sat_C1_C2_produce_0_too(
+; CHECK-NEXT: [[ADD:%.*]] = sub nuw i32 12, [[A:%.*]]
+; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[ADD]], i32 14)
+; CHECK-NEXT: ret i32 [[COND]]
+;
+ %add = sub nuw i32 12, %a
+ %cond = call i32 @llvm.usub.sat.i32(i32 %add, i32 14)
+ ret i32 %cond
+}
+
+; negative tests this souldn't work
+
+define i32 @usub_sat_C1_C2_without_nuw(i32 %a){
+; CHECK-LABEL: @usub_sat_C1_C2_without_nuw(
+; CHECK-NEXT: [[ADD:%.*]] = sub i32 12, [[A:%.*]]
+; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[ADD]], i32 14)
+; CHECK-NEXT: ret i32 [[COND]]
+;
+ %add = sub i32 12, %a
+ %cond = call i32 @llvm.usub.sat.i32(i32 %add, i32 14)
+ ret i32 %cond
+}
+
+define i32 @usub_sat_C1_C2_more_than_one_use_with_add(i32 %a){
+; CHECK-LABEL: @usub_sat_C1_C2_more_than_one_use_with_add(
+; CHECK-NEXT: [[ADD:%.*]] = sub nuw i32 12, [[A:%.*]]
+; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[ADD]], i32 14)
+; CHECK-NEXT: call void @usei32(i32 [[ADD]])
+; CHECK-NEXT: ret i32 [[COND]]
+;
+ %add = sub nuw i32 12, %a
+ %cond = call i32 @llvm.usub.sat.i32(i32 %add, i32 14)
+ call void @usei32(i32 %add)
+ ret i32 %cond
+}
+
+define i32 @usub_sat_C1_C2_more_than_one_use_with_cond(i32 %a){
+; CHECK-LABEL: @usub_sat_C1_C2_more_than_one_use_with_cond(
+; CHECK-NEXT: [[ADD:%.*]] = sub nuw i32 12, [[A:%.*]]
+; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[ADD]], i32 14)
+; CHECK-NEXT: call void @usei32(i32 [[COND]])
+; CHECK-NEXT: ret i32 [[COND]]
+;
+ %add = sub nuw i32 12, %a
+ %cond = call i32 @llvm.usub.sat.i32(i32 %add, i32 14)
+ call void @usei32(i32 %cond)
+ ret i32 %cond
+}
; (a > b) ? a - b : 0 -> usub.sat(a, b)
>From 7668aa97adc0d167883223da40f474c54ee3b61c Mon Sep 17 00:00:00 2001
From: Mohamed Atef <mohamedatef1698 at gmail.com>
Date: Mon, 19 Feb 2024 23:38:14 +0200
Subject: [PATCH 2/2] [InstCombine] Fold usub_sat((sub nuw C1, A), C2) to
usub_sat(C1 - C2, A) or 0
---
.../Transforms/InstCombine/InstCombineCalls.cpp | 17 +++++++++++++++++
.../InstCombine/unsigned_saturated_sub.ll | 11 +++--------
2 files changed, 20 insertions(+), 8 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 5266808c5abab4..7f59ad1d61d91e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2139,6 +2139,23 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
}
}
+ // usub_sat((sub nuw C1, A), C2) -> usub_sat(C1 - C2, A) if C2 u< C1
+ // usub_sat((sub nuw C1, A), C2) -> 0 otherwise
+ const APInt *C1, *C2;
+ Value *A;
+ if (IID == Intrinsic::usub_sat &&
+ match(Arg0, m_OneUse(m_NUWSub(m_APInt(C1), m_Value(A)))) &&
+ match(Arg1, m_APInt(C2)) && SI->hasOneUse()) {
+
+ if (C2->ult(*C1)) {
+ auto *New = Builder.CreateBinaryIntrinsic(
+ Intrinsic::usub_sat, ConstantInt::get(A->getType(), *C1 - *C2), A);
+ return replaceInstUsesWith(*SI, New);
+ } else {
+ return replaceInstUsesWith(*SI, ConstantInt::get(Ty, 0));
+ }
+ }
+
// ssub.sat(X, C) -> sadd.sat(X, -C) if C != MIN
Constant *C;
if (IID == Intrinsic::ssub_sat && match(Arg1, m_Constant(C)) &&
diff --git a/llvm/test/Transforms/InstCombine/unsigned_saturated_sub.ll b/llvm/test/Transforms/InstCombine/unsigned_saturated_sub.ll
index edf7c70b3c8a1a..4d60a7cc5a54bf 100644
--- a/llvm/test/Transforms/InstCombine/unsigned_saturated_sub.ll
+++ b/llvm/test/Transforms/InstCombine/unsigned_saturated_sub.ll
@@ -14,8 +14,7 @@ declare i16 @llvm.usub.sat.i16(i16, i16)
define i32 @usub_sat_C1_C2(i32 %a){
; CHECK-LABEL: @usub_sat_C1_C2(
-; CHECK-NEXT: [[ADD:%.*]] = sub nuw i32 64, [[A:%.*]]
-; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[ADD]], i32 14)
+; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.usub.sat.i32(i32 50, i32 [[A:%.*]])
; CHECK-NEXT: ret i32 [[COND]]
;
%add = sub nuw i32 64, %a
@@ -25,9 +24,7 @@ define i32 @usub_sat_C1_C2(i32 %a){
define i32 @usub_sat_C1_C2_produce_0(i32 %a){
; CHECK-LABEL: @usub_sat_C1_C2_produce_0(
-; CHECK-NEXT: [[ADD:%.*]] = sub nuw i32 14, [[A:%.*]]
-; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[ADD]], i32 14)
-; CHECK-NEXT: ret i32 [[COND]]
+; CHECK-NEXT: ret i32 0
;
%add = sub nuw i32 14, %a
%cond = call i32 @llvm.usub.sat.i32(i32 %add, i32 14)
@@ -36,9 +33,7 @@ define i32 @usub_sat_C1_C2_produce_0(i32 %a){
define i32 @usub_sat_C1_C2_produce_0_too(i32 %a){
; CHECK-LABEL: @usub_sat_C1_C2_produce_0_too(
-; CHECK-NEXT: [[ADD:%.*]] = sub nuw i32 12, [[A:%.*]]
-; CHECK-NEXT: [[COND:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[ADD]], i32 14)
-; CHECK-NEXT: ret i32 [[COND]]
+; CHECK-NEXT: ret i32 0
;
%add = sub nuw i32 12, %a
%cond = call i32 @llvm.usub.sat.i32(i32 %add, i32 14)
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