[PATCH] D135662: [ARM] Support fp16/bf16 using w constraint

Sam Elliott via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Tue Oct 11 06:02:37 PDT 2022


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fp16 and bf16 values can be used in GCC's inline assembly using the "w"
constraint, which means "VFP floating-point registers d0-d31" - fp16 and
bf16 values are stored in S registers (which alias the D registers).

This change ensures that LLVM is compatible with GCC for programs that
use fp16 and the 'w' constraint.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D135662

Files:
  llvm/lib/Target/ARM/ARMISelLowering.cpp
  llvm/test/CodeGen/ARM/inlineasm-fp-half.ll


Index: llvm/test/CodeGen/ARM/inlineasm-fp-half.ll
===================================================================
--- llvm/test/CodeGen/ARM/inlineasm-fp-half.ll
+++ llvm/test/CodeGen/ARM/inlineasm-fp-half.ll
@@ -3,8 +3,8 @@
 ; RUN: llc -mtriple=thumb -mattr=+armv8.2-a,+fp-armv8,+fullfp16,+bf16,-neon %s -o - | FileCheck %s
 
 
-define arm_aapcscc half @f(half %x) nounwind {
-; CHECK-LABEL: f:
+define arm_aapcscc half @f_t(half %x) nounwind {
+; CHECK-LABEL: f_t:
 ; CHECK:       @ %bb.0: @ %entry
 ; CHECK-NEXT:    vmov.f16 s0, r0
 ; CHECK-NEXT:    @APP
@@ -17,8 +17,22 @@
   ret half %0
 }
 
-define arm_aapcscc bfloat @h(bfloat %x) nounwind {
-; CHECK-LABEL: h:
+define arm_aapcscc half @f_w(half %x) nounwind {
+; CHECK-LABEL: f_w:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    vmov.f16 s0, r0
+; CHECK-NEXT:    @APP
+; CHECK-NEXT:    vsqrt.f16 s0, s0
+; CHECK-NEXT:    @NO_APP
+; CHECK-NEXT:    vmov r0, s0
+; CHECK-NEXT:    bx lr
+entry:
+  %0 = tail call half asm "vsqrt.f16 $0, $1", "=w,w"(half %x)
+  ret half %0
+}
+
+define arm_aapcscc bfloat @h_t(bfloat %x) nounwind {
+; CHECK-LABEL: h_t:
 ; CHECK:       @ %bb.0: @ %entry
 ; CHECK-NEXT:    vmov.f16 s0, r0
 ; CHECK-NEXT:    @APP
@@ -30,3 +44,17 @@
   %0 = tail call bfloat asm "vmov.f32 $0, $1", "=t,t"(bfloat %x)
   ret bfloat %0
 }
+
+define arm_aapcscc bfloat @h_w(bfloat %x) nounwind {
+; CHECK-LABEL: h_w:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    vmov.f16 s0, r0
+; CHECK-NEXT:    @APP
+; CHECK-NEXT:    vmov.f32 s0, s0
+; CHECK-NEXT:    @NO_APP
+; CHECK-NEXT:    vmov.f16 r0, s0
+; CHECK-NEXT:    bx lr
+entry:
+  %0 = tail call bfloat asm "vmov.f32 $0, $1", "=w,w"(bfloat %x)
+  ret bfloat %0
+}
Index: llvm/lib/Target/ARM/ARMISelLowering.cpp
===================================================================
--- llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -20141,6 +20141,8 @@
     case 'w':
       if (VT == MVT::Other)
         break;
+      if (VT == MVT::f16 || VT == MVT::bf16)
+        return RCPair(0U, &ARM::HPRRegClass);
       if (VT == MVT::f32)
         return RCPair(0U, &ARM::SPRRegClass);
       if (VT.getSizeInBits() == 64)


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