[llvm] [AMDGPU] Fix FMA Combine (PR #119217)

Mon Dec 9 06:35:27 PST 2024

llvmbot wrote:




@llvm/pr-subscribers-backend-amdgpu

Author: Piotr Sobczak (piotrAMD)

<details>
<summary>Changes</summary>

Update the check in the FMA combine to check dot10-insts instead of dot7-insts.

The target of the combine, v_dot2_f32_f16, is available only if dot10-insts target feature is enabled.

The issue probably dates back to the change that split out dot10-insts out of dot7-insts.

As far as I can see, this does not affect any current targets, but if a future target has dot7-insts, but not dot10-insts that would cause a crash ("cannot select") for the input ir in the test.

---
Full diff: https://github.com/llvm/llvm-project/pull/119217.diff


2 Files Affected:

- (modified) llvm/lib/Target/AMDGPU/SIISelLowering.cpp (+1-1) 
- (added) llvm/test/CodeGen/AMDGPU/fma_combine.ll (+70) 


``````````diff

diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index f89fe8faa600ba..8dfebd36a962e1 100644
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -14696,7 +14696,7 @@ SDValue SITargetLowering::performFMACombine(SDNode *N,
   EVT VT = N->getValueType(0);
   SDLoc SL(N);
 
-  if (!Subtarget->hasDot7Insts() || VT != MVT::f32)
+  if (!Subtarget->hasDot10Insts() || VT != MVT::f32)
     return SDValue();
 
   // FMA((F32)S0.x, (F32)S1. x, FMA((F32)S0.y, (F32)S1.y, (F32)z)) ->
diff --git a/llvm/test/CodeGen/AMDGPU/fma_combine.ll b/llvm/test/CodeGen/AMDGPU/fma_combine.ll
new file mode 100644
index 00000000000000..0414018862d071
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/fma_combine.ll
@@ -0,0 +1,70 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -mattr="+dot7-insts,-dot10-insts,-dot5-insts" < %s | FileCheck %s -check-prefix=DISABLED
+; RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -mattr="+dot7-insts,+dot10-insts,-dot5-insts" < %s | FileCheck %s -check-prefix=ENABLED
+
+; Test that FMACombine is disabled for a target without dot10-insts, and enabled for a target with dot10-insts.
+
+define amdgpu_kernel void @func() {
+; DISABLED-LABEL: func:
+; DISABLED:       ; %bb.0: ; %bb
+; DISABLED-NEXT:    v_dual_mov_b32 v0, 0 :: v_dual_mov_b32 v1, 0
+; DISABLED-NEXT:    v_mov_b32_e32 v2, 0
+; DISABLED-NEXT:    s_mov_b32 vcc_lo, exec_lo
+; DISABLED-NEXT:  .LBB0_1: ; %main
+; DISABLED-NEXT:    ; =>This Inner Loop Header: Depth=1
+; DISABLED-NEXT:    ds_load_b128 v[3:6], v1
+; DISABLED-NEXT:    ds_store_b32 v1, v0
+; DISABLED-NEXT:    s_waitcnt lgkmcnt(1)
+; DISABLED-NEXT:    v_fma_mix_f32 v2, v4, v3, v2 op_sel_hi:[1,1,0]
+; DISABLED-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(NEXT) | instid1(VALU_DEP_1)
+; DISABLED-NEXT:    v_fma_mix_f32 v2, v4, v3, v2 op_sel:[1,1,0] op_sel_hi:[1,1,0]
+; DISABLED-NEXT:    v_add_f32_e32 v2, 0, v2
+; DISABLED-NEXT:    s_cbranch_vccnz .LBB0_1
+; DISABLED-NEXT:  ; %bb.2: ; %DummyReturnBlock
+; DISABLED-NEXT:    s_endpgm
+;
+; ENABLED-LABEL: func:
+; ENABLED:       ; %bb.0: ; %bb
+; ENABLED-NEXT:    v_dual_mov_b32 v0, 0 :: v_dual_mov_b32 v1, 0
+; ENABLED-NEXT:    v_mov_b32_e32 v2, 0
+; ENABLED-NEXT:    s_mov_b32 vcc_lo, exec_lo
+; ENABLED-NEXT:  .LBB0_1: ; %main
+; ENABLED-NEXT:    ; =>This Inner Loop Header: Depth=1
+; ENABLED-NEXT:    ds_load_b128 v[3:6], v1
+; ENABLED-NEXT:    ds_store_b32 v1, v0
+; ENABLED-NEXT:    s_waitcnt lgkmcnt(1)
+; ENABLED-NEXT:    v_dot2_f32_f16 v2, v4, v3, v2
+; ENABLED-NEXT:    s_delay_alu instid0(VALU_DEP_1)
+; ENABLED-NEXT:    v_add_f32_e32 v2, 0, v2
+; ENABLED-NEXT:    s_cbranch_vccnz .LBB0_1
+; ENABLED-NEXT:  ; %bb.2: ; %DummyReturnBlock
+; ENABLED-NEXT:    s_endpgm
+bb:
+  br label %main
+
+main:                        ; preds = %main, %bb
+  %.sroa.3 = phi float [ 0.000000e+00, %bb ], [ %i17, %main ]
+  %.sroa.4 = phi float [ 0.000000e+00, %bb ], [ %.sroa.3, %main ]
+  %i = load <8 x half>, ptr addrspace(3) null, align 16
+  %i1 = bitcast <8 x half> %i to i128
+  %i2 = trunc i128 %i1 to i32
+  %i3 = bitcast i32 %i2 to <2 x half>
+  %.sroa.1 = extractelement <2 x half> %i3, i64 0
+  %.sroa.2 = extractelement <2 x half> %i3, i64 1
+  %i4 = shufflevector <8 x half> %i, <8 x half> zeroinitializer, <2 x i32> <i32 2, i32 3>
+  %i5 = fpext <2 x half> %i4 to <2 x float>
+  %i6 = fpext half %.sroa.1 to float
+  %i7 = fpext half %.sroa.2 to float
+  %i8 = extractelement <2 x float> %i5, i64 0
+  %i9 = fmul contract float %i8, %i6
+  %i10 = fadd contract float %.sroa.3, %i9
+  %i11 = extractelement <2 x float> %i5, i64 1
+  %i12 = fmul contract float %i11, %i7
+  %i13 = fadd contract float %i12, %i10
+  %i14 = insertelement <2 x float> zeroinitializer, float %i13, i64 0
+  %i15 = insertelement <2 x float> %i14, float %.sroa.4, i64 1
+  %i16 = fadd <2 x float> %i15, zeroinitializer
+  store <2 x half> zeroinitializer, ptr addrspace(3) null, align 4
+  %i17 = extractelement <2 x float> %i16, i64 0
+  br label %main
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/119217
