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[TargetLowering] add tests to show effect of setcc sub->shift; NFC 

There's effectively no difference for the cases with variables.
We just trade a sub for an add on those. But the case with a
subtract from constant would require an extra move instruction
on x86, so this looks like a reasonable generic combine.

llvm-svn: 353619
This commit is contained in:
Sanjay Patel 2019-02-09 17:03:59 +00:00
parent f31cf49c58
commit 7467510453
2 changed files with 38 additions and 1 deletions
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1
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
View File

@ -3075,7 +3075,6 @@ SDValue TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
DAG.getConstant(0, dl, N0.getValueType()),
Cond);
// The shift is not valid if this is a bool (i1).
// TODO: This transform needs evidence to justify its existence.
if (N0.getNode()->hasOneUse() && OpVT.getScalarSizeInBits() != 1) {
assert(N0.getOpcode() == ISD::SUB && "Unexpected operation!");
auto &DL = DAG.getDataLayout();

38
llvm/test/CodeGen/X86/setcc-combine.ll
View File

@ -297,3 +297,41 @@ define i64 @sub_to_shift_to_add(i32 %x, i32 %y, i64 %s1, i64 %s2) {
ret i64 %r
}
define <4 x float> @sub_to_shift_to_add_vec(<4 x i32> %x, <4 x i32> %y, <4 x float> %s1, <4 x float> %s2) {
; SSE2-LABEL: sub_to_shift_to_add_vec:
; SSE2: # %bb.0:
; SSE2-NEXT: paddd %xmm1, %xmm1
; SSE2-NEXT: pcmpeqd %xmm0, %xmm1
; SSE2-NEXT: pand %xmm1, %xmm2
; SSE2-NEXT: pandn %xmm3, %xmm1
; SSE2-NEXT: por %xmm2, %xmm1
; SSE2-NEXT: movdqa %xmm1, %xmm0
; SSE2-NEXT: retq
;
; SSE41-LABEL: sub_to_shift_to_add_vec:
; SSE41: # %bb.0:
; SSE41-NEXT: paddd %xmm1, %xmm1
; SSE41-NEXT: pcmpeqd %xmm1, %xmm0
; SSE41-NEXT: blendvps %xmm0, %xmm2, %xmm3
; SSE41-NEXT: movaps %xmm3, %xmm0
; SSE41-NEXT: retq
%sub = sub <4 x i32> %x, %y
%cmp = icmp eq <4 x i32> %sub, %y
%r = select <4 x i1> %cmp, <4 x float> %s1, <4 x float> %s2
ret <4 x float> %r
}
define i64 @sub_constant_to_shift_to_add(i32 %x, i64 %s1, i64 %s2) {
; CHECK-LABEL: sub_constant_to_shift_to_add:
; CHECK: # %bb.0:
; CHECK-NEXT: movq %rsi, %rax
; CHECK-NEXT: addl %edi, %edi
; CHECK-NEXT: cmpl $42, %edi
; CHECK-NEXT: cmovneq %rdx, %rax
; CHECK-NEXT: retq
%sub = sub i32 42, %x
%cmp = icmp eq i32 %sub, %x
%r = select i1 %cmp, i64 %s1, i64 %s2
ret i64 %r
}