[llvm] [ConstraintElim] Optimize usub.sat intrinsic based on known constraints (PR #135744)

[via llvm-commits]

================
@@ -1137,12 +1137,15 @@ void State::addInfoFor(BasicBlock &BB) {
           FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
       // TODO: Check if it is possible to instead only added the min/max facts
       // when simplifying uses of the min/max intrinsics.
-      if (!isGuaranteedNotToBePoison(&I))
-        break;
+      if (isGuaranteedNotToBePoison(&I))
+        WorkList.push_back(FactOrCheck::getInstFact(DT.getNode(&BB), &I));
+      break;
+    case Intrinsic::usub_sat:
+      WorkList.push_back(
+          FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
       [[fallthrough]];
     case Intrinsic::abs:
     case Intrinsic::uadd_sat:
-    case Intrinsic::usub_sat:
       WorkList.push_back(FactOrCheck::getInstFact(DT.getNode(&BB), &I));
----------------
el-ev wrote:

Lots of tests will no longer work after #135754, is that normal?
``` diff
diff --git a/llvm/test/Transforms/ConstraintElimination/abs.ll b/llvm/test/Transforms/ConstraintElimination/abs.ll
index e09a061410f4..a49b4643ab92 100644
--- a/llvm/test/Transforms/ConstraintElimination/abs.ll
+++ b/llvm/test/Transforms/ConstraintElimination/abs.ll
@@ -5,7 +5,8 @@ define i1 @abs_int_min_is_not_poison(i32 %arg) {
 ; CHECK-LABEL: define i1 @abs_int_min_is_not_poison(
 ; CHECK-SAME: i32 [[ARG:%.*]]) {
 ; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 false)
-; CHECK-NEXT:    ret i1 true
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sge i32 [[ABS]], [[ARG]]
+; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 false)
   %cmp = icmp sge i32 %abs, %arg
@@ -16,7 +17,8 @@ define i1 @abs_int_min_is_poison(i32 %arg) {
 ; CHECK-LABEL: define i1 @abs_int_min_is_poison(
 ; CHECK-SAME: i32 [[ARG:%.*]]) {
 ; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 true)
-; CHECK-NEXT:    ret i1 true
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sge i32 [[ABS]], [[ARG]]
+; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 true)
   %cmp = icmp sge i32 %abs, %arg
@@ -28,7 +30,8 @@ define i1 @abs_plus_one(i32 %arg) {
 ; CHECK-SAME: i32 [[ARG:%.*]]) {
 ; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 true)
 ; CHECK-NEXT:    [[ABS_PLUS_ONE:%.*]] = add nsw i32 [[ABS]], 1
-; CHECK-NEXT:    ret i1 true
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sge i32 [[ABS_PLUS_ONE]], [[ARG]]
+; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 true)
   %abs_plus_one = add nsw i32 %abs, 1
@@ -41,7 +44,8 @@ define i1 @arg_minus_one_strict_less(i32 %arg) {
 ; CHECK-SAME: i32 [[ARG:%.*]]) {
 ; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 true)
 ; CHECK-NEXT:    [[ARG_MINUS_ONE:%.*]] = add nsw i32 [[ARG]], -1
-; CHECK-NEXT:    ret i1 true
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[ARG_MINUS_ONE]], [[ABS]]
+; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 true)
   %arg_minus_one = add nsw i32 %arg, -1
@@ -54,7 +58,8 @@ define i1 @arg_minus_one_strict_greater(i32 %arg) {
 ; CHECK-SAME: i32 [[ARG:%.*]]) {
 ; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 true)
 ; CHECK-NEXT:    [[ARG_MINUS_ONE:%.*]] = add nsw i32 [[ARG]], -1
-; CHECK-NEXT:    ret i1 false
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[ARG_MINUS_ONE]], [[ABS]]
+; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 true)
   %arg_minus_one = add nsw i32 %arg, -1
@@ -138,7 +143,8 @@ define i1 @abs_is_nonnegative_int_min_is_poison(i32 %arg) {
 ; CHECK-LABEL: define i1 @abs_is_nonnegative_int_min_is_poison(
 ; CHECK-SAME: i32 [[ARG:%.*]]) {
 ; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 true)
-; CHECK-NEXT:    ret i1 true
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sge i32 [[ABS]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 true)
   %cmp = icmp sge i32 %abs, 0

```

https://github.com/llvm/llvm-project/pull/135744