[llvm] [AMDGPU] Generate s_absdiff_i32 (PR #164835)
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Fri Oct 24 15:09:17 PDT 2025
https://github.com/LU-JOHN updated https://github.com/llvm/llvm-project/pull/164835
>From a371ba36c211d77e8ddccf7a9a54c346f3974158 Mon Sep 17 00:00:00 2001
From: John Lu <John.Lu at amd.com>
Date: Tue, 21 Oct 2025 15:00:47 -0500
Subject: [PATCH 1/3] Generate s_absdiff_i32
Signed-off-by: John Lu <John.Lu at amd.com>
---
llvm/lib/Target/AMDGPU/SOPInstructions.td | 8 +++++---
llvm/test/CodeGen/AMDGPU/absdiff.ll | 12 +++++++++++
llvm/test/CodeGen/AMDGPU/s_cmp_0.ll | 25 ++++++++++++++++++-----
3 files changed, 37 insertions(+), 8 deletions(-)
create mode 100644 llvm/test/CodeGen/AMDGPU/absdiff.ll
diff --git a/llvm/lib/Target/AMDGPU/SOPInstructions.td b/llvm/lib/Target/AMDGPU/SOPInstructions.td
index 84287b621fe78..220318cb6bd40 100644
--- a/llvm/lib/Target/AMDGPU/SOPInstructions.td
+++ b/llvm/lib/Target/AMDGPU/SOPInstructions.td
@@ -838,9 +838,11 @@ def S_CBRANCH_G_FORK : SOP2_Pseudo <
let SubtargetPredicate = isGFX6GFX7GFX8GFX9;
}
-let Defs = [SCC] in {
-def S_ABSDIFF_I32 : SOP2_32 <"s_absdiff_i32">;
-} // End Defs = [SCC]
+let isCommutable = 1, Defs = [SCC] in {
+def S_ABSDIFF_I32 : SOP2_32 <"s_absdiff_i32",
+ [(set i32:$sdst, (UniformUnaryFrag<abs> (sub_oneuse i32:$src0, i32:$src1)))]
+>;
+} // End isCommutable = 1, Defs = [SCC]
let SubtargetPredicate = isGFX8GFX9 in {
def S_RFE_RESTORE_B64 : SOP2_Pseudo <
diff --git a/llvm/test/CodeGen/AMDGPU/absdiff.ll b/llvm/test/CodeGen/AMDGPU/absdiff.ll
new file mode 100644
index 0000000000000..3ce58f55ff0b9
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/absdiff.ll
@@ -0,0 +1,12 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=amdgcn-amd-amdpal -mcpu=gfx900 < %s | FileCheck %s
+
+define amdgpu_ps i32 @absdiff_v1(i32 inreg %arg, i32 inreg %arg2) {
+; CHECK-LABEL: absdiff_v1:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: s_absdiff_i32 s0, s0, s1
+; CHECK-NEXT: ; return to shader part epilog
+ %diff = sub i32 %arg, %arg2
+ %res = call i32 @llvm.abs.i32(i32 %diff, i1 false)
+ ret i32 %res
+}
diff --git a/llvm/test/CodeGen/AMDGPU/s_cmp_0.ll b/llvm/test/CodeGen/AMDGPU/s_cmp_0.ll
index dd5f838b4a206..0166d7ac7ddc2 100644
--- a/llvm/test/CodeGen/AMDGPU/s_cmp_0.ll
+++ b/llvm/test/CodeGen/AMDGPU/s_cmp_0.ll
@@ -110,6 +110,21 @@ define amdgpu_ps i32 @abs32(i32 inreg %val0) {
ret i32 %zext
}
+define amdgpu_ps i32 @absdiff32(i32 inreg %val0, i32 inreg %val1) {
+; CHECK-LABEL: absdiff32:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: s_absdiff_i32 s0, s0, s1
+; CHECK-NEXT: s_cselect_b64 s[0:1], -1, 0
+; CHECK-NEXT: v_cndmask_b32_e64 v0, 0, 1, s[0:1]
+; CHECK-NEXT: v_readfirstlane_b32 s0, v0
+; CHECK-NEXT: ; return to shader part epilog
+ %diff = sub i32 %val0, %val1
+ %result = call i32 @llvm.abs.i32(i32 %diff, i1 false)
+ %cmp = icmp ne i32 %result, 0
+ %zext = zext i1 %cmp to i32
+ ret i32 %zext
+}
+
define amdgpu_ps i32 @and32(i32 inreg %val0, i32 inreg %val1) {
; CHECK-LABEL: and32:
; CHECK: ; %bb.0:
@@ -608,14 +623,14 @@ define amdgpu_ps i32 @si_pc_add_rel_offset_must_not_optimize() {
; CHECK-NEXT: s_add_u32 s0, s0, __unnamed_1 at rel32@lo+4
; CHECK-NEXT: s_addc_u32 s1, s1, __unnamed_1 at rel32@hi+12
; CHECK-NEXT: s_cmp_lg_u64 s[0:1], 0
-; CHECK-NEXT: s_cbranch_scc0 .LBB35_2
+; CHECK-NEXT: s_cbranch_scc0 .LBB36_2
; CHECK-NEXT: ; %bb.1: ; %endif
; CHECK-NEXT: s_mov_b32 s0, 1
-; CHECK-NEXT: s_branch .LBB35_3
-; CHECK-NEXT: .LBB35_2: ; %if
+; CHECK-NEXT: s_branch .LBB36_3
+; CHECK-NEXT: .LBB36_2: ; %if
; CHECK-NEXT: s_mov_b32 s0, 0
-; CHECK-NEXT: s_branch .LBB35_3
-; CHECK-NEXT: .LBB35_3:
+; CHECK-NEXT: s_branch .LBB36_3
+; CHECK-NEXT: .LBB36_3:
%cmp = icmp ne ptr addrspace(4) @1, null
br i1 %cmp, label %endif, label %if
>From 81b07036bf0f84b41923658d66e8fb821cf3aab2 Mon Sep 17 00:00:00 2001
From: John Lu <John.Lu at amd.com>
Date: Thu, 23 Oct 2025 11:14:13 -0500
Subject: [PATCH 2/3] Remove unnecessary braces
Signed-off-by: John Lu <John.Lu at amd.com>
---
llvm/lib/Target/AMDGPU/SOPInstructions.td | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/llvm/lib/Target/AMDGPU/SOPInstructions.td b/llvm/lib/Target/AMDGPU/SOPInstructions.td
index 220318cb6bd40..1931e0be15152 100644
--- a/llvm/lib/Target/AMDGPU/SOPInstructions.td
+++ b/llvm/lib/Target/AMDGPU/SOPInstructions.td
@@ -838,11 +838,10 @@ def S_CBRANCH_G_FORK : SOP2_Pseudo <
let SubtargetPredicate = isGFX6GFX7GFX8GFX9;
}
-let isCommutable = 1, Defs = [SCC] in {
+let isCommutable = 1, Defs = [SCC] in
def S_ABSDIFF_I32 : SOP2_32 <"s_absdiff_i32",
[(set i32:$sdst, (UniformUnaryFrag<abs> (sub_oneuse i32:$src0, i32:$src1)))]
>;
-} // End isCommutable = 1, Defs = [SCC]
let SubtargetPredicate = isGFX8GFX9 in {
def S_RFE_RESTORE_B64 : SOP2_Pseudo <
>From 6720b3d42aa5d40b61ad455fa64f4a2f85053226 Mon Sep 17 00:00:00 2001
From: John Lu <John.Lu at amd.com>
Date: Fri, 24 Oct 2025 17:09:04 -0500
Subject: [PATCH 3/3] Add absdiff test variations
Signed-off-by: John Lu <John.Lu at amd.com>
---
llvm/test/CodeGen/AMDGPU/absdiff.ll | 100 ++++++++++++++++++++++++++--
1 file changed, 96 insertions(+), 4 deletions(-)
diff --git a/llvm/test/CodeGen/AMDGPU/absdiff.ll b/llvm/test/CodeGen/AMDGPU/absdiff.ll
index 3ce58f55ff0b9..9cb397fb9d1c6 100644
--- a/llvm/test/CodeGen/AMDGPU/absdiff.ll
+++ b/llvm/test/CodeGen/AMDGPU/absdiff.ll
@@ -1,12 +1,104 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc -mtriple=amdgcn-amd-amdpal -mcpu=gfx900 < %s | FileCheck %s
-define amdgpu_ps i32 @absdiff_v1(i32 inreg %arg, i32 inreg %arg2) {
-; CHECK-LABEL: absdiff_v1:
+define amdgpu_ps i16 @absdiff_i16_false(i16 inreg %arg0, i16 inreg %arg1) {
+; CHECK-LABEL: absdiff_i16_false:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: s_sub_i32 s0, s0, s1
+; CHECK-NEXT: s_sext_i32_i16 s1, s0
+; CHECK-NEXT: s_sub_i32 s0, 0, s0
+; CHECK-NEXT: s_sext_i32_i16 s0, s0
+; CHECK-NEXT: s_max_i32 s0, s1, s0
+; CHECK-NEXT: ; return to shader part epilog
+ %diff = sub i16 %arg0, %arg1
+ %res = call i16 @llvm.abs.i16(i16 %diff, i1 false) ; INT_MIN input returns INT_MIN
+ ret i16 %res
+}
+
+define amdgpu_ps i16 @absdiff_i16_true(i16 inreg %arg0, i16 inreg %arg1) {
+; CHECK-LABEL: absdiff_i16_true:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: s_sub_i32 s0, s0, s1
+; CHECK-NEXT: s_sext_i32_i16 s1, s0
+; CHECK-NEXT: s_sub_i32 s0, 0, s0
+; CHECK-NEXT: s_sext_i32_i16 s0, s0
+; CHECK-NEXT: s_max_i32 s0, s1, s0
+; CHECK-NEXT: ; return to shader part epilog
+ %diff = sub i16 %arg0, %arg1
+ %res = call i16 @llvm.abs.i16(i16 %diff, i1 true) ; INT_MIN input returns poison
+ ret i16 %res
+}
+
+define amdgpu_ps i32 @absdiff_i32_false(i32 inreg %arg0, i32 inreg %arg1) {
+; CHECK-LABEL: absdiff_i32_false:
; CHECK: ; %bb.0:
; CHECK-NEXT: s_absdiff_i32 s0, s0, s1
; CHECK-NEXT: ; return to shader part epilog
- %diff = sub i32 %arg, %arg2
- %res = call i32 @llvm.abs.i32(i32 %diff, i1 false)
+ %diff = sub i32 %arg0, %arg1
+ %res = call i32 @llvm.abs.i32(i32 %diff, i1 false) ; INT_MIN input returns INT_MIN
ret i32 %res
}
+
+define amdgpu_ps i32 @absdiff_i32_true(i32 inreg %arg0, i32 inreg %arg1) {
+; CHECK-LABEL: absdiff_i32_true:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: s_absdiff_i32 s0, s0, s1
+; CHECK-NEXT: ; return to shader part epilog
+ %diff = sub i32 %arg0, %arg1
+ %res = call i32 @llvm.abs.i32(i32 %diff, i1 true) ; INT_MIN input returns poison
+ ret i32 %res
+}
+
+; Multiple uses of %diff. No benefit for using s_absdiff_i32.
+define amdgpu_ps i32 @absdiff_i32_false_multi_use(i32 inreg %arg0, i32 inreg %arg1) {
+; CHECK-LABEL: absdiff_i32_false_multi_use:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: s_sub_i32 s1, s0, s1
+; CHECK-NEXT: s_abs_i32 s0, s1
+; CHECK-NEXT: ;;#ASMSTART
+; CHECK-NEXT: ; use s1
+; CHECK-NEXT: ;;#ASMEND
+; CHECK-NEXT: ; return to shader part epilog
+ %diff = sub i32 %arg0, %arg1
+ %res = call i32 @llvm.abs.i32(i32 %diff, i1 false) ; INT_MIN input returns INT_MIN
+ call void asm "; use $0", "s"(i32 %diff)
+ ret i32 %res
+}
+
+define <2 x i32> @absdiff_2xi32_false(<2 x i32> %arg0, <2 x i32> %arg1) {
+; CHECK-LABEL: absdiff_2xi32_false:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; CHECK-NEXT: v_sub_u32_e32 v0, v0, v2
+; CHECK-NEXT: v_sub_u32_e32 v1, v1, v3
+; CHECK-NEXT: v_sub_u32_e32 v2, 0, v0
+; CHECK-NEXT: v_max_i32_e32 v0, v2, v0
+; CHECK-NEXT: v_sub_u32_e32 v2, 0, v1
+; CHECK-NEXT: v_max_i32_e32 v1, v2, v1
+; CHECK-NEXT: s_setpc_b64 s[30:31]
+ %diff = sub <2 x i32> %arg0, %arg1
+ %res = call <2 x i32> @llvm.abs.v2i32(<2 x i32> %diff, i1 false) ; INT_MIN input returns INT_MIN
+ ret <2 x i32> %res
+}
+
+define <4 x i32> @absdiff_4xi32_false(<4 x i32> %arg0, <4 x i32> %arg1) {
+; CHECK-LABEL: absdiff_4xi32_false:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; CHECK-NEXT: v_sub_u32_e32 v0, v0, v4
+; CHECK-NEXT: v_sub_u32_e32 v1, v1, v5
+; CHECK-NEXT: v_sub_u32_e32 v4, 0, v0
+; CHECK-NEXT: v_sub_u32_e32 v2, v2, v6
+; CHECK-NEXT: v_max_i32_e32 v0, v4, v0
+; CHECK-NEXT: v_sub_u32_e32 v4, 0, v1
+; CHECK-NEXT: v_sub_u32_e32 v3, v3, v7
+; CHECK-NEXT: v_max_i32_e32 v1, v4, v1
+; CHECK-NEXT: v_sub_u32_e32 v4, 0, v2
+; CHECK-NEXT: v_max_i32_e32 v2, v4, v2
+; CHECK-NEXT: v_sub_u32_e32 v4, 0, v3
+; CHECK-NEXT: v_max_i32_e32 v3, v4, v3
+; CHECK-NEXT: s_setpc_b64 s[30:31]
+ %diff = sub <4 x i32> %arg0, %arg1
+ %res = call <4 x i32> @llvm.abs.v4i32(<4 x i32> %diff, i1 false) ; INT_MIN input returns INT_MIN
+ ret <4 x i32> %res
+}
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