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AMDGPU: Raise the priority of MAD24 in instruction selection.

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Summary:
  We have seen performance regression when v_add3 is generated. The major reason is that the v_mad pattern
is broken when v_add3 is generated. We also see the register pressure increased. While we could not properly
estimate register pressure during instruction selection, we can give mad a higher priority.

In this work, we raise the priority for mad24 in selection and resolve the performance regression.

Reviewers:
  rampitec

Differential Revision:
  https://reviews.llvm.org/D56745

llvm-svn: 351273
This commit is contained in:
Changpeng Fang 2019-01-15 23:12:36 +00:00
parent d50202586a
commit 0ce911eee3
2 changed files with 28 additions and 0 deletions
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2
lib/Target/AMDGPU/AMDGPUInstructions.td
View File

@ -842,6 +842,7 @@ def cvt_flr_i32_f32 : PatFrag <
[{ (void)N; return TM.Options.NoNaNsFPMath; }]
>;
let AddedComplexity = 2 in {
class IMad24Pat<Instruction Inst, bit HasClamp = 0> : AMDGPUPat <
(add (AMDGPUmul_i24 i32:$src0, i32:$src1), i32:$src2),
!if(HasClamp, (Inst $src0, $src1, $src2, (i1 0)),
@ -853,6 +854,7 @@ class UMad24Pat<Instruction Inst, bit HasClamp = 0> : AMDGPUPat <
!if(HasClamp, (Inst $src0, $src1, $src2, (i1 0)),
(Inst $src0, $src1, $src2))
>;
} // AddedComplexity.
class RcpPat<Instruction RcpInst, ValueType vt> : AMDGPUPat <
(fdiv FP_ONE, vt:$src),

26
test/CodeGen/AMDGPU/add3.ll
View File

@ -23,6 +23,32 @@ define amdgpu_ps float @add3(i32 %a, i32 %b, i32 %c) {
ret float %bc
}
; V_MAD_U32_U24 is given higher priority.
define amdgpu_ps float @mad_no_add3(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e) {
; GFX9-LABEL: mad_no_add3:
; GFX9: ; %bb.0:
; GFX9-NEXT: v_mad_u32_u24 v0, v0, v1, v4
; GFX9-NEXT: v_mad_u32_u24 v0, v2, v3, v0
; GFX9-NEXT: ; return to shader part epilog
%a0 = shl i32 %a, 8
%a1 = lshr i32 %a0, 8
%b0 = shl i32 %b, 8
%b1 = lshr i32 %b0, 8
%mul1 = mul i32 %a1, %b1
%c0 = shl i32 %c, 8
%c1 = lshr i32 %c0, 8
%d0 = shl i32 %d, 8
%d1 = lshr i32 %d0, 8
%mul2 = mul i32 %c1, %d1
%add0 = add i32 %e, %mul1
%add1 = add i32 %mul2, %add0
%bc = bitcast i32 %add1 to float
ret float %bc
}
; ThreeOp instruction variant not used due to Constant Bus Limitations
; TODO: with reassociation it is possible to replace a v_add_u32_e32 with a s_add_i32
define amdgpu_ps float @add3_vgpr_b(i32 inreg %a, i32 %b, i32 inreg %c) {