maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[InstCombine] try to canonicalize icmp with trunc op into mask and cmp 

The motivating test is based on:
https://llvm.org/PR52260

We have better analysis for X == 0, so try harder to form that.
This commit is contained in:
Sanjay Patel 2021-10-26 17:41:19 -04:00
parent e8fdd030b1
commit acabad9ff6
3 changed files with 41 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -4589,6 +4589,31 @@ Instruction *InstCombinerImpl::foldICmpEquality(ICmpInst &I) {
return nullptr;
}
static Instruction *foldICmpWithTrunc(ICmpInst &ICmp,
InstCombiner::BuilderTy &Builder) {
const ICmpInst::Predicate Pred = ICmp.getPredicate();
Value *Op0 = ICmp.getOperand(0), *Op1 = ICmp.getOperand(1);
// Try to canonicalize trunc + compare-to-constant into a mask + cmp.
// The trunc masks high bits while the compare may effectively mask low bits.
Value *X;
const APInt *C;
if (match(Op0, m_OneUse(m_Trunc(m_Value(X)))) && match(Op1, m_Power2(C))) {
if (Pred == ICmpInst::ICMP_ULT) {
// (trunc X) u< Pow2C --> (X & MaskC) == 0
unsigned SrcBits = X->getType()->getScalarSizeInBits();
unsigned DstBits = Op0->getType()->getScalarSizeInBits();
APInt MaskC = APInt::getOneBitSet(SrcBits, DstBits) - C->zext(SrcBits);
Value *And = Builder.CreateAnd(X, MaskC);
Constant *Zero = ConstantInt::getNullValue(X->getType());
return new ICmpInst(ICmpInst::ICMP_EQ, And, Zero);
}
// TODO: Handle ugt.
}
return nullptr;
}
static Instruction *foldICmpWithZextOrSext(ICmpInst &ICmp,
InstCombiner::BuilderTy &Builder) {
assert(isa<CastInst>(ICmp.getOperand(0)) && "Expected cast for operand 0");
@ -4732,6 +4757,9 @@ Instruction *InstCombinerImpl::foldICmpWithCastOp(ICmpInst &ICmp) {
return new ICmpInst(ICmp.getPredicate(), Op0Src, NewOp1);
}
if (Instruction *R = foldICmpWithTrunc(ICmp, Builder))
return R;
return foldICmpWithZextOrSext(ICmp, Builder);
}

20
llvm/test/Transforms/InstCombine/icmp-trunc.ll
View File

@ -5,8 +5,8 @@ declare void @use(i8)
define i1 @ult_2(i32 %x) {
; CHECK-LABEL: @ult_2(
; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i8
; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[T]], 2
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], 254
; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%t = trunc i32 %x to i8
@ -16,8 +16,8 @@ define i1 @ult_2(i32 %x) {
define <2 x i1> @ult_16_splat(<2 x i16> %x) {
; CHECK-LABEL: @ult_16_splat(
; CHECK-NEXT: [[T:%.*]] = trunc <2 x i16> [[X:%.*]] to <2 x i11>
; CHECK-NEXT: [[R:%.*]] = icmp ult <2 x i11> [[T]], <i11 16, i11 16>
; CHECK-NEXT: [[TMP1:%.*]] = and <2 x i16> [[X:%.*]], <i16 2032, i16 2032>
; CHECK-NEXT: [[R:%.*]] = icmp eq <2 x i16> [[TMP1]], zeroinitializer
; CHECK-NEXT: ret <2 x i1> [[R]]
;
%t = trunc <2 x i16> %x to <2 x i11>
@ -25,6 +25,8 @@ define <2 x i1> @ult_16_splat(<2 x i16> %x) {
ret <2 x i1> %r
}
; negative test - need power-of-2 constant
define i1 @ult_3(i32 %x) {
; CHECK-LABEL: @ult_3(
; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i8
@ -36,6 +38,8 @@ define i1 @ult_3(i32 %x) {
ret i1 %r
}
; negative test - no extra use allowed
define i1 @ult_2_use(i32 %x) {
; CHECK-LABEL: @ult_2_use(
; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i8
@ -53,12 +57,7 @@ define i1 @ult_2_use(i32 %x) {
define i1 @PR52260(i32 %x) {
; CHECK-LABEL: @PR52260(
; CHECK-NEXT: [[IDXPROM:%.*]] = sext i32 [[X:%.*]] to i64
; CHECK-NEXT: [[IDX:%.*]] = getelementptr inbounds [3 x i32], [3 x i32]* @a, i64 0, i64 [[IDXPROM]]
; CHECK-NEXT: [[T1:%.*]] = load i32, i32* [[IDX]], align 4
; CHECK-NEXT: [[TMP1:%.*]] = trunc i32 [[T1]] to i8
; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ult i8 [[TMP1]], 2
; CHECK-NEXT: ret i1 [[TOBOOL]]
; CHECK-NEXT: ret i1 true
;
%idxprom = sext i32 %x to i64
%idx = getelementptr inbounds [3 x i32], [3 x i32]* @a, i64 0, i64 %idxprom
@ -69,4 +68,3 @@ define i1 @PR52260(i32 %x) {
%tobool = icmp eq i8 %conv2, 0
ret i1 %tobool
}

8
llvm/test/Transforms/InstCombine/signed-truncation-check.ll
View File

@ -397,8 +397,8 @@ define i1 @positive_trunc_signbit_logical(i32 %arg) {
define i1 @positive_trunc_base(i32 %arg) {
; CHECK-LABEL: @positive_trunc_base(
; CHECK-NEXT: [[T1:%.*]] = trunc i32 [[ARG:%.*]] to i16
; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp ult i16 [[T1]], 128
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[ARG:%.*]], 65408
; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp eq i32 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[T5_SIMPLIFIED]]
;
%t1 = trunc i32 %arg to i16
@ -411,8 +411,8 @@ define i1 @positive_trunc_base(i32 %arg) {
define i1 @positive_trunc_base_logical(i32 %arg) {
; CHECK-LABEL: @positive_trunc_base_logical(
; CHECK-NEXT: [[T1:%.*]] = trunc i32 [[ARG:%.*]] to i16
; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp ult i16 [[T1]], 128
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[ARG:%.*]], 65408
; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp eq i32 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[T5_SIMPLIFIED]]
;
%t1 = trunc i32 %arg to i16