From: Roman Lebedev <lebedev.ri@gmail.com>
Date: Wed, 25 Sep 2019 22:59:59 +0000 (+0000)
Subject: [InstCombine] foldUnsignedUnderflowCheck(): one last pattern with 'sub' (PR43251)
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=810c818288fac9763ab4812d32b93905f37e2240;p=llvm

[InstCombine] foldUnsignedUnderflowCheck(): one last pattern with 'sub' (PR43251)

https://rise4fun.com/Alive/0j9

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@372930 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 6252e5d15a1..db5095b6fea 100644
--- a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1128,6 +1128,16 @@ static Value *foldUnsignedUnderflowCheck(ICmpInst *ZeroICmp,
       EqPred == ICmpInst::ICMP_EQ && !IsAnd)
     return Builder.CreateICmpULE(Base, Offset);
 
+  // Base <= Offset && (Base - Offset) != 0  -->  Base < Offset
+  if (UnsignedPred == ICmpInst::ICMP_ULE && EqPred == ICmpInst::ICMP_NE &&
+      IsAnd)
+    return Builder.CreateICmpULT(Base, Offset);
+
+  // Base > Offset || (Base - Offset) == 0  -->  Base >= Offset
+  if (UnsignedPred == ICmpInst::ICMP_UGT && EqPred == ICmpInst::ICMP_EQ &&
+      !IsAnd)
+    return Builder.CreateICmpUGE(Base, Offset);
+
   return nullptr;
 }
 
diff --git a/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll b/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll
index ad60ad98788..d46da5ec863 100644
--- a/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll
+++ b/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll
@@ -404,10 +404,8 @@ define i1 @base_ult_offset(i8 %base, i8 %offset) {
 ; CHECK-LABEL: @base_ult_offset(
 ; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i8 [[BASE:%.*]], [[OFFSET:%.*]]
 ; CHECK-NEXT:    call void @use8(i8 [[ADJUSTED]])
-; CHECK-NEXT:    [[NOT_NULL:%.*]] = icmp ne i8 [[ADJUSTED]], 0
-; CHECK-NEXT:    [[NO_UNDERFLOW:%.*]] = icmp ule i8 [[BASE]], [[OFFSET]]
-; CHECK-NEXT:    [[R:%.*]] = and i1 [[NO_UNDERFLOW]], [[NOT_NULL]]
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i8 [[BASE]], [[OFFSET]]
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %adjusted = sub i8 %base, %offset
   call void @use8(i8 %adjusted)
@@ -420,10 +418,8 @@ define i1 @base_uge_offset(i8 %base, i8 %offset) {
 ; CHECK-LABEL: @base_uge_offset(
 ; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i8 [[BASE:%.*]], [[OFFSET:%.*]]
 ; CHECK-NEXT:    call void @use8(i8 [[ADJUSTED]])
-; CHECK-NEXT:    [[NOT_NULL:%.*]] = icmp eq i8 [[ADJUSTED]], 0
-; CHECK-NEXT:    [[NO_UNDERFLOW:%.*]] = icmp ugt i8 [[BASE]], [[OFFSET]]
-; CHECK-NEXT:    [[R:%.*]] = or i1 [[NO_UNDERFLOW]], [[NOT_NULL]]
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp uge i8 [[BASE]], [[OFFSET]]
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %adjusted = sub i8 %base, %offset
   call void @use8(i8 %adjusted)