From e568120da32e6cddfb7c9bcc8eca172175fc6f51 Mon Sep 17 00:00:00 2001
From: Nikita Popov <nikita.ppv@gmail.com>
Date: Sun, 20 Oct 2019 20:19:42 +0000
Subject: [PATCH] [InstCombine] Fold uadd.sat(a, b) == 0 and usub.sat(a, b) ==
 0

This adds folds for comparing uadd.sat/usub.sat with zero:

 * uadd.sat(a, b) == 0 => a == 0 && b == 0 => (a | b) == 0
 * usub.sat(a, b) == 0 => a <= b

And inverted forms for !=.

Differential Revision: https://reviews.llvm.org/D69224

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375374 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineCompares.cpp       | 22 +++++++++++++++++++
 .../InstCombine/saturating-add-sub.ll         | 18 +++++++--------
 2 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 601295339ad..a9f64feb600 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3076,6 +3076,28 @@ Instruction *InstCombiner::foldICmpEqIntrinsicWithConstant(ICmpInst &Cmp,
     }
     break;
   }
+
+  case Intrinsic::uadd_sat: {
+    // uadd.sat(a, b) == 0  ->  (a | b) == 0
+    if (C.isNullValue()) {
+      Value *Or = Builder.CreateOr(II->getArgOperand(0), II->getArgOperand(1));
+      return replaceInstUsesWith(Cmp, Builder.CreateICmp(
+          Cmp.getPredicate(), Or, Constant::getNullValue(Ty)));
+
+    }
+    break;
+  }
+
+  case Intrinsic::usub_sat: {
+    // usub.sat(a, b) == 0  ->  a <= b
+    if (C.isNullValue()) {
+      ICmpInst::Predicate NewPred = Cmp.getPredicate() == ICmpInst::ICMP_EQ
+          ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_UGT;
+      return ICmpInst::Create(Instruction::ICmp, NewPred,
+                              II->getArgOperand(0), II->getArgOperand(1));
+    }
+    break;
+  }
   default:
     break;
   }
diff --git a/test/Transforms/InstCombine/saturating-add-sub.ll b/test/Transforms/InstCombine/saturating-add-sub.ll
index fa40baadec9..f5f719864b0 100644
--- a/test/Transforms/InstCombine/saturating-add-sub.ll
+++ b/test/Transforms/InstCombine/saturating-add-sub.ll
@@ -1158,9 +1158,9 @@ define i8 @test_scalar_uadd_sub_const(i8 %a) {
 
 define i1 @scalar_uadd_eq_zero(i8 %a, i8 %b) {
 ; CHECK-LABEL: @scalar_uadd_eq_zero(
-; CHECK-NEXT:    [[SAT:%.*]] = call i8 @llvm.uadd.sat.i8(i8 [[A:%.*]], i8 [[B:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[SAT]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    [[TMP1:%.*]] = or i8 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i8 [[TMP1]], 0
+; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   %sat = call i8 @llvm.uadd.sat.i8(i8 %a, i8 %b)
   %cmp = icmp eq i8 %sat, 0
@@ -1169,9 +1169,9 @@ define i1 @scalar_uadd_eq_zero(i8 %a, i8 %b) {
 
 define i1 @scalar_uadd_ne_zero(i8 %a, i8 %b) {
 ; CHECK-LABEL: @scalar_uadd_ne_zero(
-; CHECK-NEXT:    [[SAT:%.*]] = call i8 @llvm.uadd.sat.i8(i8 [[A:%.*]], i8 [[B:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[SAT]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    [[TMP1:%.*]] = or i8 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne i8 [[TMP1]], 0
+; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   %sat = call i8 @llvm.uadd.sat.i8(i8 %a, i8 %b)
   %cmp = icmp ne i8 %sat, 0
@@ -1180,8 +1180,7 @@ define i1 @scalar_uadd_ne_zero(i8 %a, i8 %b) {
 
 define i1 @scalar_usub_eq_zero(i8 %a, i8 %b) {
 ; CHECK-LABEL: @scalar_usub_eq_zero(
-; CHECK-NEXT:    [[SAT:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[A:%.*]], i8 [[B:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[SAT]], 0
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ule i8 [[A:%.*]], [[B:%.*]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %sat = call i8 @llvm.usub.sat.i8(i8 %a, i8 %b)
@@ -1191,8 +1190,7 @@ define i1 @scalar_usub_eq_zero(i8 %a, i8 %b) {
 
 define i1 @scalar_usub_ne_zero(i8 %a, i8 %b) {
 ; CHECK-LABEL: @scalar_usub_ne_zero(
-; CHECK-NEXT:    [[SAT:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[A:%.*]], i8 [[B:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[SAT]], 0
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i8 [[A:%.*]], [[B:%.*]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %sat = call i8 @llvm.usub.sat.i8(i8 %a, i8 %b)