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[InstCombine] Fold icmp (select c,const,arg), null if icmp arg, null can be simplified

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This patch folds icmp (select c,const,arg), null if icmp arg, null can be simplified.

Resolves llvm.org/pr48975.

Reviewed By: nikic, xbolva00

Differential Revision: https://reviews.llvm.org/D96663
This commit is contained in:
Juneyoung Lee 2021-06-21 16:50:54 +09:00
parent a6fd3be6d5
commit f69a2df9b9
2 changed files with 67 additions and 6 deletions
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22
lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -3290,14 +3290,24 @@ Instruction *InstCombinerImpl::foldICmpInstWithConstantNotInt(ICmpInst &I) {
// constant folded and the select turned into a bitwise or.
Value *Op1 = nullptr, *Op2 = nullptr;
ConstantInt *CI = nullptr;
if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(1))) {
Op1 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
auto SimplifyOp = [&](Value *V) {
Value *Op = nullptr;
if (Constant *C = dyn_cast<Constant>(V)) {
Op = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
} else if (RHSC->isNullValue()) {
// If null is being compared, check if it can be further simplified.
Op = SimplifyICmpInst(I.getPredicate(), V, RHSC, SQ);
}
return Op;
};
Op1 = SimplifyOp(LHSI->getOperand(1));
if (Op1)
CI = dyn_cast<ConstantInt>(Op1);
}
if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(2))) {
Op2 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
Op2 = SimplifyOp(LHSI->getOperand(2));
if (Op2)
CI = dyn_cast<ConstantInt>(Op2);
}
// We only want to perform this transformation if it will not lead to
// additional code. This is true if either both sides of the select

51
test/Transforms/InstCombine/assume-icmp-null-select.ll Normal file
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@ -0,0 +1,51 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -instcombine -S | FileCheck %s
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
define i8* @example(i8* dereferenceable(24) %x) {
; CHECK-LABEL: @example(
; CHECK-NEXT: [[X2:%.*]] = bitcast i8* [[X:%.*]] to {}**
; CHECK-NEXT: [[Y:%.*]] = load {}*, {}** [[X2]], align 8
; CHECK-NEXT: [[Y_IS_NULL:%.*]] = icmp ne {}* [[Y]], null
; CHECK-NEXT: call void @llvm.assume(i1 [[Y_IS_NULL]])
; CHECK-NEXT: ret i8* [[X]]
;
%x2 = bitcast i8* %x to {}**
%y = load {}*, {}** %x2, align 8
%y_is_null = icmp eq {}* %y, null
%x0 = getelementptr inbounds i8, i8* %x, i64 0
%res = select i1 %y_is_null, i8* null, i8* %x0
%nonnull = icmp ne i8* %res, null
call void @llvm.assume(i1 %nonnull)
ret i8* %res
}
; TODO: this should be folded to `ret i8* %x` as well.
define i8* @example2(i8* %x) {
; CHECK-LABEL: @example2(
; CHECK-NEXT: [[X2:%.*]] = bitcast i8* [[X:%.*]] to {}**
; CHECK-NEXT: [[Y:%.*]] = load {}*, {}** [[X2]], align 8
; CHECK-NEXT: [[Y_IS_NULL:%.*]] = icmp eq {}* [[Y]], null
; CHECK-NEXT: [[RES:%.*]] = select i1 [[Y_IS_NULL]], i8* null, i8* [[X]]
; CHECK-NEXT: [[NONNULL:%.*]] = icmp ne i8* [[RES]], null
; CHECK-NEXT: call void @llvm.assume(i1 [[NONNULL]])
; CHECK-NEXT: ret i8* [[RES]]
;
%x2 = bitcast i8* %x to {}**
%y = load {}*, {}** %x2, align 8
%y_is_null = icmp eq {}* %y, null
%x0 = getelementptr inbounds i8, i8* %x, i64 0
%res = select i1 %y_is_null, i8* null, i8* %x0
%nonnull = icmp ne i8* %res, null
call void @llvm.assume(i1 %nonnull)
ret i8* %res
}
declare void @llvm.assume(i1)