[llvm] [InstCombine] Use `m_NotForbidPoison` when folding `(X u< Y) ? -1 : (~X + Y) --> uadd.sat(~X, Y)` (PR #114345)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/114345

Alive2: https://alive2.llvm.org/ce/z/mTGCo-
We cannot reuse `~X` if `m_AllOnes` matches a vector constant with some poison elts. An alternative solution is to create a new not instead of reusing `~X`. But it doesn't worth the effort because we need to add a one-use check.

Fixes https://github.com/llvm/llvm-project/issues/113869.


>From a9958c46809ee4429ca12f4af1df2b0855bd0b7c Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Thu, 31 Oct 2024 09:51:10 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests. NFC.

---
 .../Transforms/InstCombine/saturating-add-sub.ll    | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/saturating-add-sub.ll b/llvm/test/Transforms/InstCombine/saturating-add-sub.ll
index a88fd3cc21f1bc..67d087f2093aee 100644
--- a/llvm/test/Transforms/InstCombine/saturating-add-sub.ll
+++ b/llvm/test/Transforms/InstCombine/saturating-add-sub.ll
@@ -1890,6 +1890,19 @@ define <2 x i32> @uadd_sat_not_ugt_commute_add(<2 x i32> %x, <2 x i32> %yp) {
   ret <2 x i32> %r
 }
 
+define <2 x i32> @uadd_sat_not_ugt_commute_add_partial_poison(<2 x i32> %x, <2 x i32> %yp) {
+; CHECK-LABEL: @uadd_sat_not_ugt_commute_add_partial_poison(
+; CHECK-NEXT:    [[NOTX:%.*]] = xor <2 x i32> [[X:%.*]], <i32 -1, i32 poison>
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.uadd.sat.v2i32(<2 x i32> [[YP:%.*]], <2 x i32> [[NOTX]])
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %notx = xor <2 x i32> %x, <i32 -1, i32 poison>
+  %a = add nuw <2 x i32> %yp, %notx
+  %c = icmp ugt <2 x i32> %yp, %x
+  %r = select <2 x i1> %c, <2 x i32> <i32 -1, i32 -1>, <2 x i32> %a
+  ret <2 x i32> %r
+}
+
 define i32 @uadd_sat_not_commute_select(i32 %x, i32 %y) {
 ; CHECK-LABEL: @uadd_sat_not_commute_select(
 ; CHECK-NEXT:    [[NOTX:%.*]] = xor i32 [[X:%.*]], -1

>From dee9d85dd166c8d8b94842070f9202bbc2c97d16 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Thu, 31 Oct 2024 10:52:57 +0800
Subject: [PATCH 2/2] [InstCombine] Use `m_NotForbidPoison` when folding `(X u<
 Y) ? -1 : (~X + Y) --> uadd.sat(~X, Y)`

---
 llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp  | 2 +-
 llvm/test/Transforms/InstCombine/saturating-add-sub.ll | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index c5f39a4c381ed1..b442e79377740d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1051,7 +1051,7 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
   // Strictness of the comparison is irrelevant.
   X = Cmp0;
   Y = Cmp1;
-  if (match(FVal, m_c_Add(m_Not(m_Specific(X)), m_Specific(Y)))) {
+  if (match(FVal, m_c_Add(m_NotForbidPoison(m_Specific(X)), m_Specific(Y)))) {
     // (X u< Y) ? -1 : (~X + Y) --> uadd.sat(~X, Y)
     // (X u< Y) ? -1 : (Y + ~X) --> uadd.sat(Y, ~X)
     BinaryOperator *BO = cast<BinaryOperator>(FVal);
diff --git a/llvm/test/Transforms/InstCombine/saturating-add-sub.ll b/llvm/test/Transforms/InstCombine/saturating-add-sub.ll
index 67d087f2093aee..af8a9314a08049 100644
--- a/llvm/test/Transforms/InstCombine/saturating-add-sub.ll
+++ b/llvm/test/Transforms/InstCombine/saturating-add-sub.ll
@@ -1893,7 +1893,9 @@ define <2 x i32> @uadd_sat_not_ugt_commute_add(<2 x i32> %x, <2 x i32> %yp) {
 define <2 x i32> @uadd_sat_not_ugt_commute_add_partial_poison(<2 x i32> %x, <2 x i32> %yp) {
 ; CHECK-LABEL: @uadd_sat_not_ugt_commute_add_partial_poison(
 ; CHECK-NEXT:    [[NOTX:%.*]] = xor <2 x i32> [[X:%.*]], <i32 -1, i32 poison>
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.uadd.sat.v2i32(<2 x i32> [[YP:%.*]], <2 x i32> [[NOTX]])
+; CHECK-NEXT:    [[A:%.*]] = add nuw <2 x i32> [[YP:%.*]], [[NOTX]]
+; CHECK-NEXT:    [[C:%.*]] = icmp ugt <2 x i32> [[YP]], [[X]]
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[C]], <2 x i32> <i32 -1, i32 -1>, <2 x i32> [[A]]
 ; CHECK-NEXT:    ret <2 x i32> [[R]]
 ;
   %notx = xor <2 x i32> %x, <i32 -1, i32 poison>