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AMDGPU: llvm.SI.fs.constant is a source of divergence 

Summary:
This intrinsic is used to get flat-shaded fragment shader inputs. Those are
uniform across a primitive, but a fragment shader wave may process pixels from
multiple primitives (as indicated by the prim_mask), and so that's where
divergence can arise.

Reviewers: arsenm, tstellarAMD

Subscribers: arsenm, llvm-commits

Differential Revision: http://reviews.llvm.org/D19747

llvm-svn: 268259
This commit is contained in:
Nicolai Haehnle 2016-05-02 17:37:01 +00:00
parent e951a1d739
commit 119d3d80cb
2 changed files with 23 additions and 0 deletions
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1
llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
View File

@ -260,6 +260,7 @@ static bool isIntrinsicSourceOfDivergence(const TargetIntrinsicInfo *TII,
return false;
case AMDGPUIntrinsic::SI_tid:
case AMDGPUIntrinsic::SI_fs_interp:
case AMDGPUIntrinsic::SI_fs_constant:
return true;
}
}

22
llvm/test/Analysis/DivergenceAnalysis/AMDGPU/interp-intrinsics.ll Normal file
View File

@ -0,0 +1,22 @@
; RUN: opt -mtriple amdgcn--- -analyze -divergence %s | FileCheck %s
; CHECK-LABEL: 'fs_interp'
; CHECK: DIVERGENT: %v = call float @llvm.SI.fs.interp(
define amdgpu_ps void @fs_interp(i32 inreg %prim_mask, <2 x i32> %interp_param) #1 {
%v = call float @llvm.SI.fs.interp(i32 0, i32 0, i32 %prim_mask, <2 x i32> %interp_param)
store volatile float %v, float addrspace(1)* undef
ret void
}
; CHECK-LABEL: 'fs_constant'
; CHECK: DIVERGENT: %v = call float @llvm.SI.fs.constant(
define amdgpu_ps void @fs_constant(i32 inreg %prim_mask, <2 x i32> %interp_param) #1 {
%v = call float @llvm.SI.fs.constant(i32 0, i32 0, i32 %prim_mask)
store volatile float %v, float addrspace(1)* undef
ret void
}
declare float @llvm.SI.fs.interp(i32, i32, i32, <2 x i32>) #0
declare float @llvm.SI.fs.constant(i32, i32, i32) #0
attributes #0 = { nounwind readnone }