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[InstCombine] add folds for icmp with xor mask constant 

These are the folds in Alive;
Name: xor_ult
Pre: isPowerOf2(-C1)
%xor = xor i8 %x, C1
%r = icmp ult i8 %xor, C1
=>
%r = icmp ugt i8 %x, ~C1

Name: xor_ugt
Pre: isPowerOf2(C1+1)
%xor = xor i8 %x, C1
%r = icmp ugt i8 %xor, C1
=>
%r = icmp ugt i8 %x, C1

https://rise4fun.com/Alive/Vty

The ugt case in its simplest form was already handled by DemandedBits,
but that's not ideal as shown in the multi-use test.

I'm not sure if these are all of the symmetrical folds, but I adjusted 
the existing code for one of the folds to try to show the similarities.

There's no obvious connection, but this is another preliminary step 
for PR14613...
https://bugs.llvm.org/show_bug.cgi?id=14613

llvm-svn: 341997
This commit is contained in:
Sanjay Patel 2018-09-11 22:00:15 +00:00
parent c72a7259be
commit 26725bdc50
2 changed files with 22 additions and 14 deletions
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29
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1499,16 +1499,25 @@ Instruction *InstCombiner::foldICmpXorConstant(ICmpInst &Cmp,
}
}
// (icmp ugt (xor X, C), ~C) -> (icmp ult X, C)
// iff -C is a power of 2
if (Pred == ICmpInst::ICMP_UGT && *XorC == ~C && (C + 1).isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_ULT, X, Y);
// (icmp ult (xor X, C), -C) -> (icmp uge X, C)
// iff -C is a power of 2
if (Pred == ICmpInst::ICMP_ULT && *XorC == -C && C.isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_UGE, X, Y);
// Mask constant magic can eliminate an 'xor' with unsigned compares.
if (Pred == ICmpInst::ICMP_UGT) {
// (xor X, ~C) >u C --> X <u ~C (when C+1 is a power of 2)
if (*XorC == ~C && (C + 1).isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_ULT, X, Y);
// (xor X, C) >u C --> X >u C (when C+1 is a power of 2)
if (*XorC == C && (C + 1).isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_UGT, X, Y);
}
if (Pred == ICmpInst::ICMP_ULT) {
// (xor X, -C) <u C --> X >u ~C (when C is a power of 2)
if (*XorC == -C && C.isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_UGT, X,
ConstantInt::get(X->getType(), ~C));
// (xor X, C) <u C --> X >u ~C (when -C is a power of 2)
if (*XorC == C && (-C).isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_UGT, X,
ConstantInt::get(X->getType(), ~C));
}
return nullptr;
}

7
llvm/test/Transforms/InstCombine/icmp.ll
View File

@ -2229,8 +2229,7 @@ define <2 x i1> @icmp_xor_neg4_X_uge_4_vec(<2 x i32> %X) {
define <2 x i1> @xor_ult(<2 x i8> %x) {
; CHECK-LABEL: @xor_ult(
; CHECK-NEXT: [[XOR:%.*]] = xor <2 x i8> [[X:%.*]], <i8 -4, i8 -4>
; CHECK-NEXT: [[R:%.*]] = icmp ult <2 x i8> [[XOR]], <i8 -4, i8 -4>
; CHECK-NEXT: [[R:%.*]] = icmp ugt <2 x i8> [[X:%.*]], <i8 3, i8 3>
; CHECK-NEXT: ret <2 x i1> [[R]]
;
%xor = xor <2 x i8> %x, <i8 -4, i8 -4>
@ -2242,7 +2241,7 @@ define i1 @xor_ult_extra_use(i8 %x, i8* %p) {
; CHECK-LABEL: @xor_ult_extra_use(
; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[X:%.*]], -32
; CHECK-NEXT: store i8 [[XOR]], i8* [[P:%.*]], align 1
; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[XOR]], -32
; CHECK-NEXT: [[R:%.*]] = icmp ugt i8 [[X]], 31
; CHECK-NEXT: ret i1 [[R]]
;
%xor = xor i8 %x, -32
@ -2265,7 +2264,7 @@ define i1 @xor_ugt_extra_use(i8 %x, i8* %p) {
; CHECK-LABEL: @xor_ugt_extra_use(
; CHECK-NEXT: [[XOR:%.*]] = xor i8 [[X:%.*]], 63
; CHECK-NEXT: store i8 [[XOR]], i8* [[P:%.*]], align 1
; CHECK-NEXT: [[R:%.*]] = icmp ugt i8 [[XOR]], 63
; CHECK-NEXT: [[R:%.*]] = icmp ugt i8 [[X]], 63
; CHECK-NEXT: ret i1 [[R]]
;
%xor = xor i8 %x, 63