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[Codegen] TargetLowering::SimplifySetCC(): omit urem when possible 

Summary:
This addresses the regression that is being exposed by D50222 in `test/CodeGen/X86/jump_sign.ll`
The missing fold, at least partially, looks trivial:
https://rise4fun.com/Alive/Zsln
i.e. if we are comparing with zero, and comparing the `urem`-by-non-power-of-two,
and the `urem` is of something that may at most have a single bit set (or no bits set at all),
the `urem` is not needed.

Reviewers: RKSimon, craig.topper, xbolva00, spatel

Reviewed By: xbolva00, spatel

Subscribers: xbolva00, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63390

llvm-svn: 364286
This commit is contained in:
Roman Lebedev 2019-06-25 10:01:42 +00:00
parent 0142b9ce31
commit cdd43eac4f
2 changed files with 14 additions and 14 deletions
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12
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
View File

@ -3024,6 +3024,18 @@ SDValue TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
}
}
// Given:
// icmp eq/ne (urem %x, %y), 0
// Iff %x has 0 or 1 bits set, and %y has at least 2 bits set, omit 'urem':
// icmp eq/ne %x, 0
if (N0.getOpcode() == ISD::UREM && N1C->isNullValue() &&
(Cond == ISD::SETEQ || Cond == ISD::SETNE)) {
KnownBits XKnown = DAG.computeKnownBits(N0.getOperand(0));
KnownBits YKnown = DAG.computeKnownBits(N0.getOperand(1));
if (XKnown.countMaxPopulation() == 1 && YKnown.countMinPopulation() >= 2)
return DAG.getSetCC(dl, VT, N0.getOperand(0), N1, Cond);
}
if (SDValue V =
optimizeSetCCOfSignedTruncationCheck(VT, N0, N1, Cond, DCI, dl))
return V;

16
llvm/test/CodeGen/X86/omit-urem-of-power-of-two-or-zero-when-comparing-with-zero.ll
View File

@ -14,14 +14,7 @@
define i1 @p0_scalar_urem_by_const(i32 %x, i32 %y) {
; CHECK-LABEL: p0_scalar_urem_by_const:
; CHECK: # %bb.0:
; CHECK-NEXT: # kill: def $edi killed $edi def $rdi
; CHECK-NEXT: andl $128, %edi
; CHECK-NEXT: movl $2863311531, %eax # imm = 0xAAAAAAAB
; CHECK-NEXT: imulq %rdi, %rax
; CHECK-NEXT: shrq $34, %rax
; CHECK-NEXT: addl %eax, %eax
; CHECK-NEXT: leal (%rax,%rax,2), %eax
; CHECK-NEXT: cmpl %eax, %edi
; CHECK-NEXT: testb $-128, %dil
; CHECK-NEXT: sete %al
; CHECK-NEXT: retq
%t0 = and i32 %x, 128 ; clearly a power-of-two or zero
@ -33,12 +26,7 @@ define i1 @p0_scalar_urem_by_const(i32 %x, i32 %y) {
define i1 @p1_scalar_urem_by_nonconst(i32 %x, i32 %y) {
; CHECK-LABEL: p1_scalar_urem_by_nonconst:
; CHECK: # %bb.0:
; CHECK-NEXT: movl %edi, %eax
; CHECK-NEXT: andl $128, %eax
; CHECK-NEXT: orl $6, %esi
; CHECK-NEXT: xorl %edx, %edx
; CHECK-NEXT: divl %esi
; CHECK-NEXT: testl %edx, %edx
; CHECK-NEXT: testb $-128, %dil
; CHECK-NEXT: sete %al
; CHECK-NEXT: retq
%t0 = and i32 %x, 128 ; clearly a power-of-two or zero