[llvm] r372930 - [InstCombine] foldUnsignedUnderflowCheck(): one last pattern with 'sub' (PR43251)

[Roman Lebedev via llvm-commits]

Author: lebedevri
Date: Wed Sep 25 15:59:59 2019
New Revision: 372930

URL: http://llvm.org/viewvc/llvm-project?rev=372930&view=rev
Log:
[InstCombine] foldUnsignedUnderflowCheck(): one last pattern with 'sub' (PR43251)

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

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
    llvm/trunk/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=372930&r1=372929&r2=372930&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Wed Sep 25 15:59:59 2019
@@ -1128,6 +1128,16 @@ static Value *foldUnsignedUnderflowCheck
       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;
 }
 

Modified: llvm/trunk/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll?rev=372930&r1=372929&r2=372930&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll Wed Sep 25 15:59:59 2019
@@ -404,10 +404,8 @@ define i1 @base_ult_offset(i8 %base, i8
 ; 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
 ; 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)