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[AMDGPU] Detect trivially uniform arguments in InstCombine #129897

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Jun 9, 2025
Merged

[AMDGPU] Detect trivially uniform arguments in InstCombine #129897

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a2b8055
[AMDGPU] Detect trivially uniform arguments in InstCombine
jayfoad Mar 5, 2025
10e1864
Add trivial uniformity tests
jayfoad Mar 5, 2025
f39a6d2
Test amdgpu_gfx i1 cases
jayfoad Mar 7, 2025
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123 changes: 123 additions & 0 deletions llvm/test/Transforms/InstCombine/AMDGPU/trivially-uniform.ll
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt -mtriple=amdgcn -mcpu=gfx1010 -passes=instcombine -S < %s | FileCheck %s

; Use readfirstlane to demonstrate when InstCombine deems an input to
; be trivially uniform.

; Constants are trivially uniform.
define i32 @test_constant() {
; CHECK-LABEL: define i32 @test_constant(
; CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
; CHECK-NEXT: ret i32 7
;
%r = call i32 @llvm.amdgcn.readfirstlane(i32 7)
ret i32 %r
}

; The result of an AlwaysUniform intrinsic is trivially uniform.
define i32 @test_intrinsic(i32 %x) {
; CHECK-LABEL: define i32 @test_intrinsic(
; CHECK-SAME: i32 [[X:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[Y:%.*]] = call i32 @llvm.amdgcn.readfirstlane.i32(i32 [[X]])
; CHECK-NEXT: ret i32 [[Y]]
;
%y = call i32 @llvm.amdgcn.readfirstlane(i32 %x)
%r = call i32 @llvm.amdgcn.readfirstlane(i32 %y)
ret i32 %r
}

; In compute kernels, all arguments are trivially uniform.

define amdgpu_kernel void @test_compute_i32(ptr %out, i32 %x) {
; CHECK-LABEL: define amdgpu_kernel void @test_compute_i32(
; CHECK-SAME: ptr [[OUT:%.*]], i32 [[X:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: store i32 [[X]], ptr [[OUT]], align 4
; CHECK-NEXT: ret void
;
%r = call i32 @llvm.amdgcn.readfirstlane(i32 %x)
store i32 %r, ptr %out
ret void
}

define amdgpu_kernel void @test_compute_i1(ptr %out, i1 %x) {
; CHECK-LABEL: define amdgpu_kernel void @test_compute_i1(
; CHECK-SAME: ptr [[OUT:%.*]], i1 [[X:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: store i1 [[X]], ptr [[OUT]], align 1
; CHECK-NEXT: ret void
;
%r = call i1 @llvm.amdgcn.readfirstlane(i1 %x)
store i1 %r, ptr %out
ret void
}

define amdgpu_kernel void @test_compute_v32i1(ptr %out, <32 x i1> %x) {
; CHECK-LABEL: define amdgpu_kernel void @test_compute_v32i1(
; CHECK-SAME: ptr [[OUT:%.*]], <32 x i1> [[X:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: store <32 x i1> [[X]], ptr [[OUT]], align 4
; CHECK-NEXT: ret void
;
%r = call <32 x i1> @llvm.amdgcn.readfirstlane(<32 x i1> %x)
store <32 x i1> %r, ptr %out
ret void
}

; In graphics shaders, inreg arguments are trivially uniform.

define amdgpu_ps i32 @test_graphics_i32(i32 inreg %x) {
; CHECK-LABEL: define amdgpu_ps i32 @test_graphics_i32(
; CHECK-SAME: i32 inreg [[X:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: ret i32 [[X]]
;
%r = call i32 @llvm.amdgcn.readfirstlane(i32 %x)
ret i32 %r
}

define amdgpu_ps i1 @test_graphics_i1(i1 inreg %x) {
; CHECK-LABEL: define amdgpu_ps i1 @test_graphics_i1(
; CHECK-SAME: i1 inreg [[X:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: ret i1 [[X]]
;
%r = call i1 @llvm.amdgcn.readfirstlane(i1 %x)
ret i1 %r
}

define amdgpu_ps <32 x i1> @test_graphics_v32i1(<32 x i1> inreg %x) {
; CHECK-LABEL: define amdgpu_ps <32 x i1> @test_graphics_v32i1(
; CHECK-SAME: <32 x i1> inreg [[X:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: ret <32 x i1> [[X]]
;
%r = call <32 x i1> @llvm.amdgcn.readfirstlane(<32 x i1> %x)
ret <32 x i1> %r
}

; In graphics shaders, non-inreg arguments are not trivially uniform.

define amdgpu_ps i32 @test_graphics_i32_negative(i32 %x) {
; CHECK-LABEL: define amdgpu_ps i32 @test_graphics_i32_negative(
; CHECK-SAME: i32 [[X:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[R:%.*]] = call i32 @llvm.amdgcn.readfirstlane.i32(i32 [[X]])
; CHECK-NEXT: ret i32 [[R]]
;
%r = call i32 @llvm.amdgcn.readfirstlane(i32 %x)
ret i32 %r
}

define amdgpu_ps i1 @test_graphics_i1_negative(i1 %x) {
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@arsenm arsenm Mar 7, 2025

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The i1 cases should use the default calling convention or amdgpu_gfx, the tricky case is non-entry function

; CHECK-LABEL: define amdgpu_ps i1 @test_graphics_i1_negative(
; CHECK-SAME: i1 [[X:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[R:%.*]] = call i1 @llvm.amdgcn.readfirstlane.i1(i1 [[X]])
; CHECK-NEXT: ret i1 [[R]]
;
%r = call i1 @llvm.amdgcn.readfirstlane(i1 %x)
ret i1 %r
}

define amdgpu_ps <32 x i1> @test_graphics_v32i1_negative(<32 x i1> %x) {
; CHECK-LABEL: define amdgpu_ps <32 x i1> @test_graphics_v32i1_negative(
; CHECK-SAME: <32 x i1> [[X:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[R:%.*]] = call <32 x i1> @llvm.amdgcn.readfirstlane.v32i1(<32 x i1> [[X]])
; CHECK-NEXT: ret <32 x i1> [[R]]
;
%r = call <32 x i1> @llvm.amdgcn.readfirstlane(<32 x i1> %x)
ret <32 x i1> %r
}