[AMDGPU] Disable inline constants for pseudo scalar transcendentals

[perlfu]

Prevent operand folding from inlining constants into pseudo scalar transcendental f16 instructions.
However still allow literal constants.

[llvmbot]

@llvm/pr-subscribers-backend-amdgpu

Author: Carl Ritson (perlfu)

Changes

Prevent operand folding from inlining constants into pseudo scalar transcendental f16 instructions.
However still allow literal constants.

---

Full diff: https://github.com/llvm/llvm-project/pull/104395.diff

3 Files Affected:

• (modified) llvm/lib/Target/AMDGPU/GCNSubtarget.h (+6)
• (modified) llvm/lib/Target/AMDGPU/SIInstrInfo.cpp (+12)
• (added) llvm/test/CodeGen/AMDGPU/pseudo-scalar-transcendental.mir (+120)

diff --git a/llvm/lib/Target/AMDGPU/GCNSubtarget.h b/llvm/lib/Target/AMDGPU/GCNSubtarget.h
index def89c785b855..902f51ae358d5 100644
--- a/llvm/lib/Target/AMDGPU/GCNSubtarget.h
+++ b/llvm/lib/Target/AMDGPU/GCNSubtarget.h
@@ -1289,6 +1289,12 @@ class GCNSubtarget final : public AMDGPUGenSubtargetInfo,
   /// and STOREcnt rather than VMcnt, LGKMcnt and VScnt respectively.
   bool hasExtendedWaitCounts() const { return getGeneration() >= GFX12; }
 
+  /// \returns true if inline constants are not supported for F16 pseudo
+  /// scalar transcendentals.
+  bool hasNoF16PseudoScalarTransInlineConstants() const {
+    return getGeneration() == GFX12;
+  }
+
   /// \returns The maximum number of instructions that can be enclosed in an
   /// S_CLAUSE on the given subtarget, or 0 for targets that do not support that
   /// instruction.
diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
index 9147242046ced..9ee65e390317a 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -5776,6 +5776,18 @@ bool SIInstrInfo::isOperandLegal(const MachineInstr &MI, unsigned OpIdx,
           return false;
       }
     }
+  } else if (isVOP3(MI) && ST.hasNoF16PseudoScalarTransInlineConstants() &&
+             !MO->isReg() && isInlineConstant(*MO, OpInfo)) {
+    switch (MI.getOpcode()) {
+    case AMDGPU::V_S_EXP_F16_e64:
+    case AMDGPU::V_S_LOG_F16_e64:
+    case AMDGPU::V_S_RCP_F16_e64:
+    case AMDGPU::V_S_RSQ_F16_e64:
+    case AMDGPU::V_S_SQRT_F16_e64:
+      return false;
+    default:
+      break;
+    }
   }
 
   if (MO->isReg()) {
diff --git a/llvm/test/CodeGen/AMDGPU/pseudo-scalar-transcendental.mir b/llvm/test/CodeGen/AMDGPU/pseudo-scalar-transcendental.mir
new file mode 100644
index 0000000000000..17bed38bd046d
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/pseudo-scalar-transcendental.mir
@@ -0,0 +1,120 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=amdgcn-amd-amdpal -mcpu=gfx1200 -run-pass=si-fold-operands -verify-machineinstrs -o - %s | FileCheck --check-prefix=GCN %s
+
+# Do not use inline constants for f16 pseudo scalar transcendentals.
+# But allow literal constants.
+
+---
+name: exp_f16_imm
+tracksRegLiveness: true
+body: |
+  bb.0:
+    ; GCN-LABEL: name: exp_f16_imm
+    ; GCN: [[S_MOV_B32_:%[0-9]+]]:sgpr_32 = S_MOV_B32 15360
+    ; GCN-NEXT: [[V_S_EXP_F16_e64_:%[0-9]+]]:sgpr_32 = V_S_EXP_F16_e64 1, [[S_MOV_B32_]], 0, 0, implicit $mode, implicit $exec
+    %0:sgpr_32 = S_MOV_B32 15360
+    %1:sgpr_32 = V_S_EXP_F16_e64 1, %0:sgpr_32, 0, 0, implicit $mode, implicit $exec
+...
+
+---
+name: exp_f16_literal
+tracksRegLiveness: true
+body: |
+  bb.0:
+    ; GCN-LABEL: name: exp_f16_literal
+    ; GCN: [[V_S_EXP_F16_e64_:%[0-9]+]]:sgpr_32 = V_S_EXP_F16_e64 1, 16960, 0, 0, implicit $mode, implicit $exec
+    %0:sgpr_32 = S_MOV_B32 16960
+    %1:sgpr_32 = V_S_EXP_F16_e64 1, %0:sgpr_32, 0, 0, implicit $mode, implicit $exec
+...
+
+---
+name: log_f16_imm
+tracksRegLiveness: true
+body: |
+  bb.0:
+    ; GCN-LABEL: name: log_f16_imm
+    ; GCN: [[S_MOV_B32_:%[0-9]+]]:sgpr_32 = S_MOV_B32 15360
+    ; GCN-NEXT: [[V_S_LOG_F16_e64_:%[0-9]+]]:sgpr_32 = V_S_LOG_F16_e64 1, [[S_MOV_B32_]], 0, 0, implicit $mode, implicit $exec
+    %0:sgpr_32 = S_MOV_B32 15360
+    %1:sgpr_32 = V_S_LOG_F16_e64 1, %0:sgpr_32, 0, 0, implicit $mode, implicit $exec
+...
+
+---
+name: log_f16_literal
+tracksRegLiveness: true
+body: |
+  bb.0:
+    ; GCN-LABEL: name: log_f16_literal
+    ; GCN: [[V_S_LOG_F16_e64_:%[0-9]+]]:sgpr_32 = V_S_LOG_F16_e64 1, 16960, 0, 0, implicit $mode, implicit $exec
+    %0:sgpr_32 = S_MOV_B32 16960
+    %1:sgpr_32 = V_S_LOG_F16_e64 1, %0:sgpr_32, 0, 0, implicit $mode, implicit $exec
+...
+
+---
+name: rcp_f16_imm
+tracksRegLiveness: true
+body: |
+  bb.0:
+    ; GCN-LABEL: name: rcp_f16_imm
+    ; GCN: [[S_MOV_B32_:%[0-9]+]]:sgpr_32 = S_MOV_B32 15360
+    ; GCN-NEXT: [[V_S_RCP_F16_e64_:%[0-9]+]]:sgpr_32 = V_S_RCP_F16_e64 1, [[S_MOV_B32_]], 0, 0, implicit $mode, implicit $exec
+    %0:sgpr_32 = S_MOV_B32 15360
+    %1:sgpr_32 = V_S_RCP_F16_e64 1, %0:sgpr_32, 0, 0, implicit $mode, implicit $exec
+...
+
+---
+name: rcp_f16_literal
+tracksRegLiveness: true
+body: |
+  bb.0:
+    ; GCN-LABEL: name: rcp_f16_literal
+    ; GCN: [[V_S_RCP_F16_e64_:%[0-9]+]]:sgpr_32 = V_S_RCP_F16_e64 1, 16960, 0, 0, implicit $mode, implicit $exec
+    %0:sgpr_32 = S_MOV_B32 16960
+    %1:sgpr_32 = V_S_RCP_F16_e64 1, %0:sgpr_32, 0, 0, implicit $mode, implicit $exec
+...
+
+---
+name: rsq_f16_imm
+tracksRegLiveness: true
+body: |
+  bb.0:
+    ; GCN-LABEL: name: rsq_f16_imm
+    ; GCN: [[S_MOV_B32_:%[0-9]+]]:sgpr_32 = S_MOV_B32 15360
+    ; GCN-NEXT: [[V_S_RSQ_F16_e64_:%[0-9]+]]:sgpr_32 = V_S_RSQ_F16_e64 1, [[S_MOV_B32_]], 0, 0, implicit $mode, implicit $exec
+    %0:sgpr_32 = S_MOV_B32 15360
+    %1:sgpr_32 = V_S_RSQ_F16_e64 1, %0:sgpr_32, 0, 0, implicit $mode, implicit $exec
+...
+
+---
+name: rsq_f16_literal
+tracksRegLiveness: true
+body: |
+  bb.0:
+    ; GCN-LABEL: name: rsq_f16_literal
+    ; GCN: [[V_S_RSQ_F16_e64_:%[0-9]+]]:sgpr_32 = V_S_RSQ_F16_e64 1, 16960, 0, 0, implicit $mode, implicit $exec
+    %0:sgpr_32 = S_MOV_B32 16960
+    %1:sgpr_32 = V_S_RSQ_F16_e64 1, %0:sgpr_32, 0, 0, implicit $mode, implicit $exec
+...
+
+---
+name: sqrt_f16_imm
+tracksRegLiveness: true
+body: |
+  bb.0:
+    ; GCN-LABEL: name: sqrt_f16_imm
+    ; GCN: [[S_MOV_B32_:%[0-9]+]]:sgpr_32 = S_MOV_B32 15360
+    ; GCN-NEXT: [[V_S_SQRT_F16_e64_:%[0-9]+]]:sgpr_32 = V_S_SQRT_F16_e64 1, [[S_MOV_B32_]], 0, 0, implicit $mode, implicit $exec
+    %0:sgpr_32 = S_MOV_B32 15360
+    %1:sgpr_32 = V_S_SQRT_F16_e64 1, %0:sgpr_32, 0, 0, implicit $mode, implicit $exec
+...
+
+---
+name: sqrt_f16_literal
+tracksRegLiveness: true
+body: |
+  bb.0:
+    ; GCN-LABEL: name: sqrt_f16_literal
+    ; GCN: [[V_S_SQRT_F16_e64_:%[0-9]+]]:sgpr_32 = V_S_SQRT_F16_e64 1, 16960, 0, 0, implicit $mode, implicit $exec
+    %0:sgpr_32 = S_MOV_B32 16960
+    %1:sgpr_32 = V_S_SQRT_F16_e64 1, %0:sgpr_32, 0, 0, implicit $mode, implicit $exec
+...

[arsenm]

ST.hasNoF16PseudoScalarTransInlineConstants() && isVOP3(MI) are both redundant with the opcode check. Move the opcode switch into an isF16PseudoScalarTrans helper?

[perlfu]

ST.hasNoF16PseudoScalarTransInlineConstants() is still required as this can be architecture specific.
Moved the rest to a helper.

[arsenm]

lgtm with nit

[jayfoad]

@perlfu can you get this merged into the 19.x branch please?

[perlfu]

/cherry-pick fc6300a

[llvmbot]

/pull-request #105472