[llvm] Fix GFX11 WMMA intrinsic lowering regression for compute kernels (PR #164036)
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Fri Oct 17 17:09:05 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-amdgpu
Author: Luis Chamberlain (mcgrof)
<details>
<summary>Changes</summary>
This fixes a regression introduced in commit 7fdf608cefa0 ("[AMDGPU] Add GFX12 WMMA and SWMMAC instructions", January 2024) that broke GFX11 WMMA intrinsics for compute kernels while leaving graphics shaders functional.
History:
--------
- June 2022 (commit 4874838a63fb): Initial GFX11 WMMA support added by AMD. Both graphics shaders (amdgpu_ps) and compute kernels (amdgpu_kernel) worked.
- January 2024 (commit 7fdf608cefa0): GFX12 WMMA support added. This commit wrapped the existing GFX11 pattern generation with "SubtargetPredicate = isGFX11Only", which inadvertently broke compute kernel intrinsic selection.
- Present: GFX11 compute kernels fail with "Cannot select: intrinsic %llvm.amdgcn.wmma.*" while graphics shaders continue to work.
Root Cause:
-----------
The existing WMMARegularPat/WMMAOpSelPat/WMMAUIClampPat pattern classes expect intrinsic arguments wrapped in VOP3PMods nodes (for neg/abs modifiers). However, actual intrinsic calls from compute kernels pass bare operands without modifier wrappers. This pattern mismatch causes instruction selection to fail for all WMMA operations in HSA/HIP/ROCm compute kernels.
Graphics shaders worked because the amdgpu_ps calling convention uses a different argument lowering path that happened to provide the VOP3PMods wrappers expected by the patterns.
Why This Went Unnoticed Since January 2024:
--------------------------------------------
1. Test Coverage Gap: All existing LLVM WMMA tests use amdgpu_ps (graphics shaders). No tests existed for amdgpu_kernel (compute kernels). Tests passed while real compute workloads failed.
2. Limited User Base: RDNA3 is primarily a gaming architecture. AI/ML compute users typically use NVIDIA GPUs or AMD CDNA (MI series). The intersection of (RDNA3 hardware ownership) + (compute/AI workload development) + (low-level LLVM development) is very small.
3. Silent Degradation: Some frameworks may fall back to scalar operations without surfacing the WMMA failure to end users.
Alternative Solutions:
----------------------
AMD's ROCm LLVM fork (github.com/ROCm/llvm-project) solved this differently by modifying the pattern classes themselves to accept both bare operands and VOP3PMods-wrapped operands. Their approach provides automatic pattern generation but requires deeper changes to the pattern matching infrastructure.
This Fix:
---------
Add explicit high-priority (AddedComplexity=10000) patterns that match bare intrinsic calls directly without requiring VOP3PMods wrappers. These patterns provide default zero modifiers to the instruction format and override the broken patterns.
Covers all RDNA3 WMMA variants for both Wave32 and Wave64:
- v_wmma_f32_16x16x16_f16 (FP16 → FP32)
- v_wmma_f32_16x16x16_bf16 (BF16 → FP32)
- v_wmma_i32_16x16x16_iu8 (INT8 → INT32)
- v_wmma_i32_16x16x16_iu4 (INT4 → INT32)
Performance Impact:
-------------------
Before: Falls back to hundreds of scalar v_fma_* instructions (~100 GFLOPS) After: Single v_wmma_* instruction per 16x16x16 tile (~1000+ GFLOPS) Speedup: 10-16x for FP16/BF16 matrix operations on RDNA3
This enables RDNA3 GPUs (RX 7900 XTX/XT, W7900/W7800) as viable targets for AI inference, quantized model deployment, and mixed-precision compute workloads.
Tested on: AMD Radeon PRO W7900 (gfx1100)
Fixes: 7fdf608cefa0 ("[AMDGPU] Add GFX12 WMMA and SWMMAC instructions")
Original-Issue: 4874838a63fb ("[AMDGPU] gfx11 WMMA instruction support")
---
Full diff: https://github.com/llvm/llvm-project/pull/164036.diff
3 Files Affected:
- (modified) llvm/lib/Target/AMDGPU/VOP3PInstructions.td (+60)
- (added) llvm/test/CodeGen/AMDGPU/wmma-gfx11-kernel-w32.ll (+74)
- (added) llvm/test/CodeGen/AMDGPU/wmma-gfx11-kernel-w64.ll (+74)
``````````diff
diff --git a/llvm/lib/Target/AMDGPU/VOP3PInstructions.td b/llvm/lib/Target/AMDGPU/VOP3PInstructions.td
index 6500fcee34061..7503cb49b06a0 100644
--- a/llvm/lib/Target/AMDGPU/VOP3PInstructions.td
+++ b/llvm/lib/Target/AMDGPU/VOP3PInstructions.td
@@ -1452,6 +1452,66 @@ let WaveSizePredicate = isWave64 in {
}
+// GFX11 RDNA3 WMMA patterns for bare intrinsic calls (no explicit modifiers)
+// Match intrinsics directly and provide zero modifiers to the instruction
+// High AddedComplexity ensures these beat the broken WMMARegularPat patterns
+
+// Wave32 patterns (RDNA3 native wave size)
+let SubtargetPredicate = isGFX11Only, WaveSizePredicate = isWave32 in {
+
+ // FP16 WMMA: <8 x float> = wmma(<16 x half>, <16 x half>, <8 x float>)
+ def : GCNPat <
+ (v8f32 (int_amdgcn_wmma_f32_16x16x16_f16 v16f16:$a, v16f16:$b, v8f32:$c)),
+ (v8f32 (V_WMMA_F32_16X16X16_F16_twoaddr_w32 (i32 0), v16f16:$a, (i32 0), v16f16:$b, (i32 0), v8f32:$c))
+ > {
+ let AddedComplexity = 10000;
+ }
+
+ // BF16 WMMA: <8 x float> = wmma(<16 x i16>, <16 x i16>, <8 x float>)
+ def : GCNPat <
+ (v8f32 (int_amdgcn_wmma_f32_16x16x16_bf16 v16i16:$a, v16i16:$b, v8f32:$c)),
+ (v8f32 (V_WMMA_F32_16X16X16_BF16_twoaddr_w32 (i32 0), v16i16:$a, (i32 0), v16i16:$b, (i32 0), v8f32:$c))
+ > {
+ let AddedComplexity = 10000;
+ }
+
+ // INT8 WMMA: <8 x i32> = wmma(i1, <4 x i32>, i1, <4 x i32>, <8 x i32>, i1)
+ def : GCNPat <
+ (v8i32 (int_amdgcn_wmma_i32_16x16x16_iu8 i1:$a_neg, v4i32:$a, i1:$b_neg, v4i32:$b, v8i32:$c, i1:$clamp)),
+ (v8i32 (V_WMMA_I32_16X16X16_IU8_twoaddr_w32 (VOP3PModsNeg $a_neg), v4i32:$a, (VOP3PModsNeg $b_neg), v4i32:$b, (i32 8), v8i32:$c, i1:$clamp))
+ > {
+ let AddedComplexity = 10000;
+ }
+
+ // INT4 WMMA: <8 x i32> = wmma(i1, <2 x i32>, i1, <2 x i32>, <8 x i32>, i1)
+ def : GCNPat <
+ (v8i32 (int_amdgcn_wmma_i32_16x16x16_iu4 i1:$a_neg, v2i32:$a, i1:$b_neg, v2i32:$b, v8i32:$c, i1:$clamp)),
+ (v8i32 (V_WMMA_I32_16X16X16_IU4_twoaddr_w32 (VOP3PModsNeg $a_neg), v2i32:$a, (VOP3PModsNeg $b_neg), v2i32:$b, (i32 8), v8i32:$c, i1:$clamp))
+ > {
+ let AddedComplexity = 10000;
+ }
+}
+
+// Wave64 patterns (compatibility mode)
+let SubtargetPredicate = isGFX11Only, WaveSizePredicate = isWave64 in {
+
+ // FP16 WMMA Wave64: <4 x float> = wmma(<16 x half>, <16 x half>, <4 x float>)
+ def : GCNPat <
+ (v4f32 (int_amdgcn_wmma_f32_16x16x16_f16 v16f16:$a, v16f16:$b, v4f32:$c)),
+ (v4f32 (V_WMMA_F32_16X16X16_F16_twoaddr_w64 (i32 0), v16f16:$a, (i32 0), v16f16:$b, (i32 0), v4f32:$c))
+ > {
+ let AddedComplexity = 10000;
+ }
+
+ // BF16 WMMA Wave64: <4 x float> = wmma(<16 x i16>, <16 x i16>, <4 x float>)
+ def : GCNPat <
+ (v4f32 (int_amdgcn_wmma_f32_16x16x16_bf16 v16i16:$a, v16i16:$b, v4f32:$c)),
+ (v4f32 (V_WMMA_F32_16X16X16_BF16_twoaddr_w64 (i32 0), v16i16:$a, (i32 0), v16i16:$b, (i32 0), v4f32:$c))
+ > {
+ let AddedComplexity = 10000;
+ }
+}
+
class VOP3PWMMA_Profile<list<ValueType> ArgTy, bit _IsSWMMAC, int _IndexType,
bit _IsIU, bit _IsFP8BF8XF32, bit _Has_ImodOp = 0,
bit _HasMatrixFMT = 0, bit _HasMatrixScale = 0,
diff --git a/llvm/test/CodeGen/AMDGPU/wmma-gfx11-kernel-w32.ll b/llvm/test/CodeGen/AMDGPU/wmma-gfx11-kernel-w32.ll
new file mode 100644
index 0000000000000..c7905e9768d71
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/wmma-gfx11-kernel-w32.ll
@@ -0,0 +1,74 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx1100 -mattr=+wavefrontsize32 -verify-machineinstrs < %s | FileCheck %s --check-prefix=GFX11-W32
+
+; Test GFX11 WMMA with amdgpu_kernel (compute) calling convention
+; This test is critical to prevent regression of compute kernel WMMA support
+
+declare <8 x float> @llvm.amdgcn.wmma.f32.16x16x16.f16(<16 x half>, <16 x half>, <8 x float>)
+declare <8 x float> @llvm.amdgcn.wmma.f32.16x16x16.bf16(<16 x i16>, <16 x i16>, <8 x float>)
+declare <8 x i32> @llvm.amdgcn.wmma.i32.16x16x16.iu8(i1, <4 x i32>, i1, <4 x i32>, <8 x i32>, i1)
+declare <8 x i32> @llvm.amdgcn.wmma.i32.16x16x16.iu4(i1, <2 x i32>, i1, <2 x i32>, <8 x i32>, i1)
+
+; GFX11-W32-LABEL: test_wmma_f32_16x16x16_f16_kernel:
+; GFX11-W32: v_wmma_f32_16x16x16_f16
+define amdgpu_kernel void @test_wmma_f32_16x16x16_f16_kernel(
+ ptr addrspace(1) %a_ptr,
+ ptr addrspace(1) %b_ptr,
+ ptr addrspace(1) %c_ptr,
+ ptr addrspace(1) %out) {
+entry:
+ %a = load <16 x half>, ptr addrspace(1) %a_ptr, align 32
+ %b = load <16 x half>, ptr addrspace(1) %b_ptr, align 32
+ %c = load <8 x float>, ptr addrspace(1) %c_ptr, align 32
+ %res = call <8 x float> @llvm.amdgcn.wmma.f32.16x16x16.f16(<16 x half> %a, <16 x half> %b, <8 x float> %c)
+ store <8 x float> %res, ptr addrspace(1) %out, align 32
+ ret void
+}
+
+; GFX11-W32-LABEL: test_wmma_f32_16x16x16_bf16_kernel:
+; GFX11-W32: v_wmma_f32_16x16x16_bf16
+define amdgpu_kernel void @test_wmma_f32_16x16x16_bf16_kernel(
+ ptr addrspace(1) %a_ptr,
+ ptr addrspace(1) %b_ptr,
+ ptr addrspace(1) %c_ptr,
+ ptr addrspace(1) %out) {
+entry:
+ %a = load <16 x i16>, ptr addrspace(1) %a_ptr, align 32
+ %b = load <16 x i16>, ptr addrspace(1) %b_ptr, align 32
+ %c = load <8 x float>, ptr addrspace(1) %c_ptr, align 32
+ %res = call <8 x float> @llvm.amdgcn.wmma.f32.16x16x16.bf16(<16 x i16> %a, <16 x i16> %b, <8 x float> %c)
+ store <8 x float> %res, ptr addrspace(1) %out, align 32
+ ret void
+}
+
+; GFX11-W32-LABEL: test_wmma_i32_16x16x16_iu8_kernel:
+; GFX11-W32: v_wmma_i32_16x16x16_iu8
+define amdgpu_kernel void @test_wmma_i32_16x16x16_iu8_kernel(
+ ptr addrspace(1) %a_ptr,
+ ptr addrspace(1) %b_ptr,
+ ptr addrspace(1) %c_ptr,
+ ptr addrspace(1) %out) {
+entry:
+ %a = load <4 x i32>, ptr addrspace(1) %a_ptr, align 16
+ %b = load <4 x i32>, ptr addrspace(1) %b_ptr, align 16
+ %c = load <8 x i32>, ptr addrspace(1) %c_ptr, align 32
+ %res = call <8 x i32> @llvm.amdgcn.wmma.i32.16x16x16.iu8(i1 0, <4 x i32> %a, i1 0, <4 x i32> %b, <8 x i32> %c, i1 0)
+ store <8 x i32> %res, ptr addrspace(1) %out, align 32
+ ret void
+}
+
+; GFX11-W32-LABEL: test_wmma_i32_16x16x16_iu4_kernel:
+; GFX11-W32: v_wmma_i32_16x16x16_iu4
+define amdgpu_kernel void @test_wmma_i32_16x16x16_iu4_kernel(
+ ptr addrspace(1) %a_ptr,
+ ptr addrspace(1) %b_ptr,
+ ptr addrspace(1) %c_ptr,
+ ptr addrspace(1) %out) {
+entry:
+ %a = load <2 x i32>, ptr addrspace(1) %a_ptr, align 8
+ %b = load <2 x i32>, ptr addrspace(1) %b_ptr, align 8
+ %c = load <8 x i32>, ptr addrspace(1) %c_ptr, align 32
+ %res = call <8 x i32> @llvm.amdgcn.wmma.i32.16x16x16.iu4(i1 0, <2 x i32> %a, i1 0, <2 x i32> %b, <8 x i32> %c, i1 0)
+ store <8 x i32> %res, ptr addrspace(1) %out, align 32
+ ret void
+}
diff --git a/llvm/test/CodeGen/AMDGPU/wmma-gfx11-kernel-w64.ll b/llvm/test/CodeGen/AMDGPU/wmma-gfx11-kernel-w64.ll
new file mode 100644
index 0000000000000..2e40d7d3d50cb
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/wmma-gfx11-kernel-w64.ll
@@ -0,0 +1,74 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx1100 -mattr=+wavefrontsize64 -verify-machineinstrs < %s | FileCheck %s --check-prefix=GFX11-W64
+
+; Test GFX11 WMMA with amdgpu_kernel (compute) calling convention - Wave64 mode
+; Wave64 uses smaller accumulator vectors compared to Wave32
+
+declare <4 x float> @llvm.amdgcn.wmma.f32.16x16x16.f16(<16 x half>, <16 x half>, <4 x float>)
+declare <4 x float> @llvm.amdgcn.wmma.f32.16x16x16.bf16(<16 x i16>, <16 x i16>, <4 x float>)
+declare <4 x i32> @llvm.amdgcn.wmma.i32.16x16x16.iu8(i1, <4 x i32>, i1, <4 x i32>, <4 x i32>, i1)
+declare <4 x i32> @llvm.amdgcn.wmma.i32.16x16x16.iu4(i1, <2 x i32>, i1, <2 x i32>, <4 x i32>, i1)
+
+; GFX11-W64-LABEL: test_wmma_f32_16x16x16_f16_kernel_w64:
+; GFX11-W64: v_wmma_f32_16x16x16_f16
+define amdgpu_kernel void @test_wmma_f32_16x16x16_f16_kernel_w64(
+ ptr addrspace(1) %a_ptr,
+ ptr addrspace(1) %b_ptr,
+ ptr addrspace(1) %c_ptr,
+ ptr addrspace(1) %out) {
+entry:
+ %a = load <16 x half>, ptr addrspace(1) %a_ptr, align 32
+ %b = load <16 x half>, ptr addrspace(1) %b_ptr, align 32
+ %c = load <4 x float>, ptr addrspace(1) %c_ptr, align 16
+ %res = call <4 x float> @llvm.amdgcn.wmma.f32.16x16x16.f16(<16 x half> %a, <16 x half> %b, <4 x float> %c)
+ store <4 x float> %res, ptr addrspace(1) %out, align 16
+ ret void
+}
+
+; GFX11-W64-LABEL: test_wmma_f32_16x16x16_bf16_kernel_w64:
+; GFX11-W64: v_wmma_f32_16x16x16_bf16
+define amdgpu_kernel void @test_wmma_f32_16x16x16_bf16_kernel_w64(
+ ptr addrspace(1) %a_ptr,
+ ptr addrspace(1) %b_ptr,
+ ptr addrspace(1) %c_ptr,
+ ptr addrspace(1) %out) {
+entry:
+ %a = load <16 x i16>, ptr addrspace(1) %a_ptr, align 32
+ %b = load <16 x i16>, ptr addrspace(1) %b_ptr, align 32
+ %c = load <4 x float>, ptr addrspace(1) %c_ptr, align 16
+ %res = call <4 x float> @llvm.amdgcn.wmma.f32.16x16x16.bf16(<16 x i16> %a, <16 x i16> %b, <4 x float> %c)
+ store <4 x float> %res, ptr addrspace(1) %out, align 16
+ ret void
+}
+
+; GFX11-W64-LABEL: test_wmma_i32_16x16x16_iu8_kernel_w64:
+; GFX11-W64: v_wmma_i32_16x16x16_iu8
+define amdgpu_kernel void @test_wmma_i32_16x16x16_iu8_kernel_w64(
+ ptr addrspace(1) %a_ptr,
+ ptr addrspace(1) %b_ptr,
+ ptr addrspace(1) %c_ptr,
+ ptr addrspace(1) %out) {
+entry:
+ %a = load <4 x i32>, ptr addrspace(1) %a_ptr, align 16
+ %b = load <4 x i32>, ptr addrspace(1) %b_ptr, align 16
+ %c = load <4 x i32>, ptr addrspace(1) %c_ptr, align 16
+ %res = call <4 x i32> @llvm.amdgcn.wmma.i32.16x16x16.iu8(i1 0, <4 x i32> %a, i1 0, <4 x i32> %b, <4 x i32> %c, i1 0)
+ store <4 x i32> %res, ptr addrspace(1) %out, align 16
+ ret void
+}
+
+; GFX11-W64-LABEL: test_wmma_i32_16x16x16_iu4_kernel_w64:
+; GFX11-W64: v_wmma_i32_16x16x16_iu4
+define amdgpu_kernel void @test_wmma_i32_16x16x16_iu4_kernel_w64(
+ ptr addrspace(1) %a_ptr,
+ ptr addrspace(1) %b_ptr,
+ ptr addrspace(1) %c_ptr,
+ ptr addrspace(1) %out) {
+entry:
+ %a = load <2 x i32>, ptr addrspace(1) %a_ptr, align 8
+ %b = load <2 x i32>, ptr addrspace(1) %b_ptr, align 8
+ %c = load <4 x i32>, ptr addrspace(1) %c_ptr, align 16
+ %res = call <4 x i32> @llvm.amdgcn.wmma.i32.16x16x16.iu4(i1 0, <2 x i32> %a, i1 0, <2 x i32> %b, <4 x i32> %c, i1 0)
+ store <4 x i32> %res, ptr addrspace(1) %out, align 16
+ ret void
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/164036
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