[Mesa-dev] [PATCH 1/2] radv: flush f32->f16 conversion denormals to zero. (v2)

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

SPIR-V defines the f32->f16 operation as flushing denormals to 0,
this compares the class using amd class opcode.

Thanks to Matt Arsenault for figuring it out.

This fix is VI+ only, add a TODO for SI/CIK.

This fixes:
dEQP-VK.spirv_assembly.instruction.compute.opquantize.flush_to_zero

Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 src/amd/common/ac_nir_to_llvm.c | 32 ++++++++++++++++++++++++++++----
 src/amd/common/sid.h            | 13 +++++++++++++
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/src/amd/common/ac_nir_to_llvm.c b/src/amd/common/ac_nir_to_llvm.c
index 15974a7..6c28e98 100644
--- a/src/amd/common/ac_nir_to_llvm.c
+++ b/src/amd/common/ac_nir_to_llvm.c
@@ -1022,6 +1022,33 @@ static LLVMValueRef emit_b2f(struct nir_to_llvm_context *ctx,
 	return LLVMBuildAnd(ctx->builder, src0, LLVMBuildBitCast(ctx->builder, LLVMConstReal(ctx->f32, 1.0), ctx->i32, ""), "");
 }
 
+static LLVMValueRef emit_f2f16(struct nir_to_llvm_context *ctx,
+			       LLVMValueRef src0)
+{
+	LLVMValueRef result;
+	LLVMValueRef cond;
+
+	src0 = to_float(ctx, src0);
+	result = LLVMBuildFPTrunc(ctx->builder, src0, ctx->f16, "");
+
+	/* TODO SI/CIK options here */
+	if (ctx->options->chip_class >= VI) {
+		LLVMValueRef args[2];
+		/* Check if the result is a denormal - and flush to 0 if so. */
+		args[0] = result;
+		args[1] = LLVMConstInt(ctx->i32, N_SUBNORMAL | P_SUBNORMAL, false);
+		cond = ac_build_intrinsic(&ctx->ac, "llvm.amdgcn.class.f16", ctx->i1, args, 2, AC_FUNC_ATTR_READNONE);
+	}
+
+	/* need to convert back up to f32 */
+	result = LLVMBuildFPExt(ctx->builder, result, ctx->f32, "");
+
+	if (ctx->options->chip_class >= VI)
+		result = LLVMBuildSelect(ctx->builder, cond, ctx->f32zero, result, "");
+
+	return result;
+}
+
 static LLVMValueRef emit_umul_high(struct nir_to_llvm_context *ctx,
 				   LLVMValueRef src0, LLVMValueRef src1)
 {
@@ -1520,10 +1547,7 @@ static void visit_alu(struct nir_to_llvm_context *ctx, nir_alu_instr *instr)
 		result = emit_b2f(ctx, src[0]);
 		break;
 	case nir_op_fquantize2f16:
-		src[0] = to_float(ctx, src[0]);
-		result = LLVMBuildFPTrunc(ctx->builder, src[0], ctx->f16, "");
-		/* need to convert back up to f32 */
-		result = LLVMBuildFPExt(ctx->builder, result, ctx->f32, "");
+		result = emit_f2f16(ctx, src[0]);
 		break;
 	case nir_op_umul_high:
 		result = emit_umul_high(ctx, src[0], src[1]);
diff --git a/src/amd/common/sid.h b/src/amd/common/sid.h
index 7789add..fa20690 100644
--- a/src/amd/common/sid.h
+++ b/src/amd/common/sid.h
@@ -9063,5 +9063,18 @@
 #define    CIK_SDMA_PACKET_SRBM_WRITE              0xe
 #define    CIK_SDMA_COPY_MAX_SIZE                  0x3fffe0
 
+enum amd_cmp_class_flags {
+	S_NAN = 1 << 0,        // Signaling NaN
+	Q_NAN = 1 << 1,        // Quiet NaN
+	N_INFINITY = 1 << 2,   // Negative infinity
+	N_NORMAL = 1 << 3,     // Negative normal
+	N_SUBNORMAL = 1 << 4,  // Negative subnormal
+	N_ZERO = 1 << 5,       // Negative zero
+	P_ZERO = 1 << 6,       // Positive zero
+	P_SUBNORMAL = 1 << 7,  // Positive subnormal
+	P_NORMAL = 1 << 8,     // Positive normal
+	P_INFINITY = 1 << 9    // Positive infinity
+};
+
 #endif /* _SID_H */
 
-- 
2.9.3