[llvm] r372768 - [InstCombine] (a+b) < a && (a+b) != 0 -> (0-b) < a iff a/b != 0 (PR43259)
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Tue Sep 24 09:10:50 PDT 2019
Author: lebedevri
Date: Tue Sep 24 09:10:50 2019
New Revision: 372768
URL: http://llvm.org/viewvc/llvm-project?rev=372768&view=rev
Log:
[InstCombine] (a+b) < a && (a+b) != 0 -> (0-b) < a iff a/b != 0 (PR43259)
Summary:
This is again motivated by D67122 sanitizer check enhancement.
That patch seemingly worsens `-fsanitize=pointer-overflow`
overhead from 25% to 50%, which strongly implies missing folds.
For
```
#include <cassert>
char* test(char& base, signed long offset) {
__builtin_assume(offset < 0);
return &base + offset;
}
```
We produce
https://godbolt.org/z/r40U47
and again those two icmp's can be merged:
```
Name: 0
Pre: C != 0
%adjusted = add i8 %base, C
%not_null = icmp ne i8 %adjusted, 0
%no_underflow = icmp ult i8 %adjusted, %base
%r = and i1 %not_null, %no_underflow
=>
%neg_offset = sub i8 0, C
%r = icmp ugt i8 %base, %neg_offset
```
https://rise4fun.com/Alive/ALap
https://rise4fun.com/Alive/slnN
There are 3 other variants of this pattern,
i believe they all will go into InstSimplify.
https://bugs.llvm.org/show_bug.cgi?id=43259
Reviewers: spatel, xbolva00, nikic
Reviewed By: spatel
Subscribers: efriedma, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D67849
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
llvm/trunk/test/Transforms/InstCombine/result-of-add-of-negative-is-non-zero-and-no-underflow.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=372768&r1=372767&r2=372768&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Tue Sep 24 09:10:50 2019
@@ -1061,6 +1061,10 @@ static Value *foldUnsignedUnderflowCheck
!ICmpInst::isEquality(EqPred))
return nullptr;
+ auto IsKnownNonZero = [&](Value *V) {
+ return isKnownNonZero(V, Q.DL, /*Depth=*/0, Q.AC, Q.CxtI, Q.DT);
+ };
+
ICmpInst::Predicate UnsignedPred;
Value *A, *B;
@@ -1071,15 +1075,32 @@ static Value *foldUnsignedUnderflowCheck
if (UnsignedICmp->getOperand(0) != ZeroCmpOp)
UnsignedPred = ICmpInst::getSwappedPredicate(UnsignedPred);
+ auto GetKnownNonZeroAndOther = [&](Value *&NonZero, Value *&Other) {
+ if (!IsKnownNonZero(NonZero))
+ std::swap(NonZero, Other);
+ return IsKnownNonZero(NonZero);
+ };
+
// Given ZeroCmpOp = (A + B)
// ZeroCmpOp <= A && ZeroCmpOp != 0 --> (0-B) < A
// ZeroCmpOp > A || ZeroCmpOp == 0 --> (0-B) >= A
+ //
+ // ZeroCmpOp < A && ZeroCmpOp != 0 --> (0-X) < Y iff
+ // ZeroCmpOp >= A || ZeroCmpOp == 0 --> (0-X) >= Y iff
+ // with X being the value (A/B) that is known to be non-zero,
+ // and Y being remaining value.
if (UnsignedPred == ICmpInst::ICMP_ULE && EqPred == ICmpInst::ICMP_NE &&
IsAnd)
return Builder.CreateICmpULT(Builder.CreateNeg(B), A);
+ if (UnsignedPred == ICmpInst::ICMP_ULT && EqPred == ICmpInst::ICMP_NE &&
+ IsAnd && GetKnownNonZeroAndOther(B, A))
+ return Builder.CreateICmpULT(Builder.CreateNeg(B), A);
if (UnsignedPred == ICmpInst::ICMP_UGT && EqPred == ICmpInst::ICMP_EQ &&
!IsAnd)
return Builder.CreateICmpUGE(Builder.CreateNeg(B), A);
+ if (UnsignedPred == ICmpInst::ICMP_UGE && EqPred == ICmpInst::ICMP_EQ &&
+ !IsAnd && GetKnownNonZeroAndOther(B, A))
+ return Builder.CreateICmpUGE(Builder.CreateNeg(B), A);
}
Value *Base, *Offset;
@@ -1094,12 +1115,10 @@ static Value *foldUnsignedUnderflowCheck
UnsignedPred = ICmpInst::getSwappedPredicate(UnsignedPred);
if (UnsignedPred == ICmpInst::ICMP_ULT && IsAnd &&
- EqPred == ICmpInst::ICMP_NE &&
- isKnownNonZero(Offset, Q.DL, /*Depth=*/0, Q.AC, Q.CxtI, Q.DT))
+ EqPred == ICmpInst::ICMP_NE && IsKnownNonZero(Offset))
return Builder.CreateICmpUGT(Base, Offset);
if (UnsignedPred == ICmpInst::ICMP_UGE && !IsAnd &&
- EqPred == ICmpInst::ICMP_EQ &&
- isKnownNonZero(Offset, Q.DL, /*Depth=*/0, Q.AC, Q.CxtI, Q.DT))
+ EqPred == ICmpInst::ICMP_EQ && IsKnownNonZero(Offset))
return Builder.CreateICmpULE(Base, Offset);
}
Modified: llvm/trunk/test/Transforms/InstCombine/result-of-add-of-negative-is-non-zero-and-no-underflow.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/result-of-add-of-negative-is-non-zero-and-no-underflow.ll?rev=372768&r1=372767&r2=372768&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/result-of-add-of-negative-is-non-zero-and-no-underflow.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/result-of-add-of-negative-is-non-zero-and-no-underflow.ll Tue Sep 24 09:10:50 2019
@@ -31,10 +31,9 @@ define i1 @t1(i8 %base, i8 %offset) {
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[ADJUSTED:%.*]] = add i8 [[BASE]], [[OFFSET:%.*]]
; CHECK-NEXT: call void @use8(i8 [[ADJUSTED]])
-; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp ne i8 [[ADJUSTED]], 0
-; CHECK-NEXT: [[NO_UNDERFLOW:%.*]] = icmp ult i8 [[ADJUSTED]], [[BASE]]
-; CHECK-NEXT: [[R:%.*]] = and i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: [[TMP1:%.*]] = sub i8 0, [[BASE]]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp ult i8 [[TMP1]], [[OFFSET]]
+; CHECK-NEXT: ret i1 [[TMP2]]
;
%cmp = icmp slt i8 %base, 0
call void @llvm.assume(i1 %cmp)
@@ -54,10 +53,9 @@ define i1 @t2(i8 %base, i8 %offset) {
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[ADJUSTED:%.*]] = add i8 [[BASE:%.*]], [[OFFSET]]
; CHECK-NEXT: call void @use8(i8 [[ADJUSTED]])
-; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp ne i8 [[ADJUSTED]], 0
-; CHECK-NEXT: [[NO_UNDERFLOW:%.*]] = icmp ult i8 [[ADJUSTED]], [[BASE]]
-; CHECK-NEXT: [[R:%.*]] = and i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: [[TMP1:%.*]] = sub i8 0, [[OFFSET]]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp ult i8 [[TMP1]], [[BASE]]
+; CHECK-NEXT: ret i1 [[TMP2]]
;
%cmp = icmp slt i8 %offset, 0
call void @llvm.assume(i1 %cmp)
@@ -79,9 +77,9 @@ define i1 @t3_oneuse0(i8 %base, i8 %offs
; CHECK-NEXT: call void @use8(i8 [[ADJUSTED]])
; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp ne i8 [[ADJUSTED]], 0
; CHECK-NEXT: call void @use1(i1 [[NOT_NULL]])
-; CHECK-NEXT: [[NO_UNDERFLOW:%.*]] = icmp ult i8 [[ADJUSTED]], [[BASE]]
-; CHECK-NEXT: [[R:%.*]] = and i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: [[TMP1:%.*]] = sub i8 0, [[BASE]]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp ult i8 [[TMP1]], [[OFFSET]]
+; CHECK-NEXT: ret i1 [[TMP2]]
;
%cmp = icmp slt i8 %base, 0
call void @llvm.assume(i1 %cmp)
@@ -100,11 +98,11 @@ define i1 @t4_oneuse1(i8 %base, i8 %offs
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[ADJUSTED:%.*]] = add i8 [[BASE]], [[OFFSET:%.*]]
; CHECK-NEXT: call void @use8(i8 [[ADJUSTED]])
-; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp ne i8 [[ADJUSTED]], 0
; CHECK-NEXT: [[NO_UNDERFLOW:%.*]] = icmp ult i8 [[ADJUSTED]], [[BASE]]
; CHECK-NEXT: call void @use1(i1 [[NO_UNDERFLOW]])
-; CHECK-NEXT: [[R:%.*]] = and i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: [[TMP1:%.*]] = sub i8 0, [[BASE]]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp ult i8 [[TMP1]], [[OFFSET]]
+; CHECK-NEXT: ret i1 [[TMP2]]
;
%cmp = icmp slt i8 %base, 0
call void @llvm.assume(i1 %cmp)
@@ -149,10 +147,9 @@ define i1 @t6_commutativity0(i8 %base, i
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[ADJUSTED:%.*]] = add i8 [[BASE]], [[OFFSET:%.*]]
; CHECK-NEXT: call void @use8(i8 [[ADJUSTED]])
-; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp ne i8 [[ADJUSTED]], 0
-; CHECK-NEXT: [[NO_UNDERFLOW:%.*]] = icmp ult i8 [[ADJUSTED]], [[BASE]]
-; CHECK-NEXT: [[R:%.*]] = and i1 [[NO_UNDERFLOW]], [[NOT_NULL]]
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: [[TMP1:%.*]] = sub i8 0, [[BASE]]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp ult i8 [[TMP1]], [[OFFSET]]
+; CHECK-NEXT: ret i1 [[TMP2]]
;
%cmp = icmp slt i8 %base, 0
call void @llvm.assume(i1 %cmp)
@@ -170,10 +167,9 @@ define i1 @t7_commutativity1(i8 %base, i
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[ADJUSTED:%.*]] = add i8 [[BASE]], [[OFFSET:%.*]]
; CHECK-NEXT: call void @use8(i8 [[ADJUSTED]])
-; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp ne i8 [[ADJUSTED]], 0
-; CHECK-NEXT: [[NO_UNDERFLOW:%.*]] = icmp ult i8 [[ADJUSTED]], [[BASE]]
-; CHECK-NEXT: [[R:%.*]] = and i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: [[TMP1:%.*]] = sub i8 0, [[BASE]]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp ult i8 [[TMP1]], [[OFFSET]]
+; CHECK-NEXT: ret i1 [[TMP2]]
;
%cmp = icmp slt i8 %base, 0
call void @llvm.assume(i1 %cmp)
@@ -191,10 +187,9 @@ define i1 @t7_commutativity3(i8 %base, i
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[ADJUSTED:%.*]] = add i8 [[BASE]], [[OFFSET:%.*]]
; CHECK-NEXT: call void @use8(i8 [[ADJUSTED]])
-; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp ne i8 [[ADJUSTED]], 0
-; CHECK-NEXT: [[NO_UNDERFLOW:%.*]] = icmp ult i8 [[ADJUSTED]], [[BASE]]
-; CHECK-NEXT: [[R:%.*]] = and i1 [[NO_UNDERFLOW]], [[NOT_NULL]]
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: [[TMP1:%.*]] = sub i8 0, [[BASE]]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp ult i8 [[TMP1]], [[OFFSET]]
+; CHECK-NEXT: ret i1 [[TMP2]]
;
%cmp = icmp slt i8 %base, 0
call void @llvm.assume(i1 %cmp)
@@ -214,10 +209,9 @@ define i1 @t8(i8 %base, i8 %offset) {
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[ADJUSTED:%.*]] = add i8 [[BASE]], [[OFFSET:%.*]]
; CHECK-NEXT: call void @use8(i8 [[ADJUSTED]])
-; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp eq i8 [[ADJUSTED]], 0
-; CHECK-NEXT: [[NO_UNDERFLOW:%.*]] = icmp uge i8 [[ADJUSTED]], [[BASE]]
-; CHECK-NEXT: [[R:%.*]] = or i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: [[TMP1:%.*]] = sub i8 0, [[BASE]]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp uge i8 [[TMP1]], [[OFFSET]]
+; CHECK-NEXT: ret i1 [[TMP2]]
;
%cmp = icmp slt i8 %base, 0
call void @llvm.assume(i1 %cmp)
@@ -237,10 +231,9 @@ define i1 @t9(i8 %base, i8 %offset) {
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[ADJUSTED:%.*]] = add i8 [[BASE]], [[OFFSET:%.*]]
; CHECK-NEXT: call void @use8(i8 [[ADJUSTED]])
-; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp ne i8 [[ADJUSTED]], 0
-; CHECK-NEXT: [[NO_UNDERFLOW:%.*]] = icmp ult i8 [[ADJUSTED]], [[OFFSET]]
-; CHECK-NEXT: [[R:%.*]] = and i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: [[TMP1:%.*]] = sub i8 0, [[BASE]]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp ult i8 [[TMP1]], [[OFFSET]]
+; CHECK-NEXT: ret i1 [[TMP2]]
;
%cmp = icmp slt i8 %base, 0
call void @llvm.assume(i1 %cmp)
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