[clang] [clang-tools-extra] [llvm] [ConstraintElim] Add facts implied by llvm.abs (PR #73189)

[Alexander Shaposhnikov via cfe-commits]

https://github.com/alexander-shaposhnikov updated https://github.com/llvm/llvm-project/pull/73189

>From a9e76a878edc8bc9cb81b8aa169bbbc467d32026 Mon Sep 17 00:00:00 2001
From: Alexander Shaposhnikov <ashaposhnikov at google.com>
Date: Thu, 23 Nov 2023 00:37:08 +0000
Subject: [PATCH] [ConstraintElim] Add a fact implied by llvm.abs

---
 .../Scalar/ConstraintElimination.cpp          | 10 +++++++
 .../Transforms/ConstraintElimination/abs.ll   | 26 +++++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 llvm/test/Transforms/ConstraintElimination/abs.ll

diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index 7aadd810c1da3..59aaa677ccbf9 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -995,6 +995,11 @@ void State::addInfoFor(BasicBlock &BB) {
       continue;
     }
 
+    if (match(&I, m_Intrinsic<Intrinsic::abs>())) {
+      WorkList.push_back(FactOrCheck::getInstFact(DT.getNode(&BB), &I));
+      continue;
+    }
+
     Value *A, *B;
     CmpInst::Predicate Pred;
     // For now, just handle assumes with a single compare as condition.
@@ -1629,6 +1634,11 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT, LoopInfo &LI,
 
     ICmpInst::Predicate Pred;
     if (!CB.isConditionFact()) {
+      if (Value *X; match(CB.Inst, m_Intrinsic<Intrinsic::abs>(m_Value(X)))) {
+        AddFact(CmpInst::ICMP_SGE, CB.Inst, X);
+        continue;
+      }
+
       if (auto *MinMax = dyn_cast<MinMaxIntrinsic>(CB.Inst)) {
         Pred = ICmpInst::getNonStrictPredicate(MinMax->getPredicate());
         AddFact(Pred, MinMax, MinMax->getLHS());
diff --git a/llvm/test/Transforms/ConstraintElimination/abs.ll b/llvm/test/Transforms/ConstraintElimination/abs.ll
new file mode 100644
index 0000000000000..1cf56c6e37a8c
--- /dev/null
+++ b/llvm/test/Transforms/ConstraintElimination/abs.ll
@@ -0,0 +1,26 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -passes=constraint-elimination -S %s | FileCheck %s
+
+define i1 @abs_false(i32 %arg) {
+; CHECK-LABEL: define i1 @abs_false(
+; CHECK-SAME: i32 [[ARG:%.*]]) {
+; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 false)
+; CHECK-NEXT:    ret i1 true
+;
+  %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 false)
+  %cmp = icmp sge i32 %abs, %arg
+  ret i1 %cmp
+}
+
+define i1 @abs_true(i32 %arg) {
+; CHECK-LABEL: define i1 @abs_true(
+; CHECK-SAME: i32 [[ARG:%.*]]) {
+; CHECK-NEXT:    [[ABS:%.*]] = tail call i32 @llvm.abs.i32(i32 [[ARG]], i1 true)
+; CHECK-NEXT:    ret i1 true
+;
+  %abs = tail call i32 @llvm.abs.i32(i32 %arg, i1 true)
+  %cmp = icmp sge i32 %abs, %arg
+  ret i1 %cmp
+}
+
+declare i32 @llvm.abs.i32(i32, i1 immarg)