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[x86] fold sext (xor Bool, -1) --> sub (zext Bool), 1 

This is the same transform that is current used for:
select Bool, 0, -1

llvm-svn: 295568
This commit is contained in:
Sanjay Patel 2017-02-18 21:03:28 +00:00
parent 079d511891
commit 12c2093e1e
2 changed files with 22 additions and 22 deletions
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10
llvm/lib/Target/X86/X86ISelLowering.cpp
View File

@ -33436,6 +33436,16 @@ static SDValue combineSext(SDNode *N, SelectionDAG &DAG,
return SDValue();
}
if (InVT == MVT::i1 && N0.getOpcode() == ISD::XOR &&
isAllOnesConstant(N0.getOperand(1)) && N0.hasOneUse()) {
// Invert and sign-extend a boolean is the same as zero-extend and subtract
// 1 because 0 becomes -1 and 1 becomes 0. The subtract is efficiently
// lowered with an LEA or a DEC. This is the same as: select Bool, 0, -1.
// sext (xor Bool, -1) --> sub (zext Bool), 1
SDValue Zext = DAG.getNode(ISD::ZERO_EXTEND, DL, VT, N0.getOperand(0));
return DAG.getNode(ISD::SUB, DL, VT, Zext, DAG.getConstant(1, DL, VT));
}
if (SDValue V = combineToExtendVectorInReg(N, DAG, DCI, Subtarget))
return V;

34
llvm/test/CodeGen/X86/sext-i1.ll
View File

@ -117,19 +117,16 @@ define i64 @t5(i32 %x) nounwind readnone ssp {
define i32 @select_0_or_1s(i1 %cond) {
; X32-LABEL: select_0_or_1s:
; X32: # BB#0:
; X32-NEXT: movb {{[0-9]+}}(%esp), %al
; X32-NEXT: notb %al
; X32-NEXT: movzbl %al, %eax
; X32-NEXT: movzbl {{[0-9]+}}(%esp), %eax
; X32-NEXT: andl $1, %eax
; X32-NEXT: negl %eax
; X32-NEXT: decl %eax
; X32-NEXT: retl
;
; X64-LABEL: select_0_or_1s:
; X64: # BB#0:
; X64-NEXT: notb %dil
; X64-NEXT: movzbl %dil, %eax
; X64-NEXT: andl $1, %eax
; X64-NEXT: negl %eax
; X64-NEXT: # kill: %EDI<def> %EDI<kill> %RDI<def>
; X64-NEXT: andl $1, %edi
; X64-NEXT: leal -1(%rdi), %eax
; X64-NEXT: retq
%not = xor i1 %cond, 1
%sext = sext i1 %not to i32
@ -141,19 +138,14 @@ define i32 @select_0_or_1s(i1 %cond) {
define i32 @select_0_or_1s_zeroext(i1 zeroext %cond) {
; X32-LABEL: select_0_or_1s_zeroext:
; X32: # BB#0:
; X32-NEXT: movb {{[0-9]+}}(%esp), %al
; X32-NEXT: notb %al
; X32-NEXT: movzbl %al, %eax
; X32-NEXT: andl $1, %eax
; X32-NEXT: negl %eax
; X32-NEXT: movzbl {{[0-9]+}}(%esp), %eax
; X32-NEXT: decl %eax
; X32-NEXT: retl
;
; X64-LABEL: select_0_or_1s_zeroext:
; X64: # BB#0:
; X64-NEXT: notb %dil
; X64-NEXT: movzbl %dil, %eax
; X64-NEXT: andl $1, %eax
; X64-NEXT: negl %eax
; X64-NEXT: decl %eax
; X64-NEXT: retq
%not = xor i1 %cond, 1
%sext = sext i1 %not to i32
@ -166,18 +158,16 @@ define i32 @select_0_or_1s_signext(i1 signext %cond) {
; X32-LABEL: select_0_or_1s_signext:
; X32: # BB#0:
; X32-NEXT: movb {{[0-9]+}}(%esp), %al
; X32-NEXT: notb %al
; X32-NEXT: andb $1, %al
; X32-NEXT: movzbl %al, %eax
; X32-NEXT: andl $1, %eax
; X32-NEXT: negl %eax
; X32-NEXT: decl %eax
; X32-NEXT: retl
;
; X64-LABEL: select_0_or_1s_signext:
; X64: # BB#0:
; X64-NEXT: notb %dil
; X64-NEXT: andb $1, %dil
; X64-NEXT: movzbl %dil, %eax
; X64-NEXT: andl $1, %eax
; X64-NEXT: negl %eax
; X64-NEXT: decl %eax
; X64-NEXT: retq
%not = xor i1 %cond, 1
%sext = sext i1 %not to i32