Mesa (17.3): radv: use a faster version for nir_op_pack_half_2x16

[Emil Velikov]

Module: Mesa
Branch: 17.3
Commit: ef9b0b1ab2d57bb3386c2044dd57a31b4ec38cb4
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=ef9b0b1ab2d57bb3386c2044dd57a31b4ec38cb4

Author: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Date:   Tue Dec  5 18:02:08 2017 +0100

radv: use a faster version for nir_op_pack_half_2x16

This patch is ported from RadeonSI and it has two effects.

It fixes a rendering issue which affects F1 2017 and Dawn
of War 3 (Vega only) because LLVM was ending up by generating
the new v_mad_mix_{hi,lo} instructions which appear to be
buggy in some way. Not sure if Mesa is generating something
wrong or if the issue is in LLVM only. Anyway, that explains why
the DOW3 issue can't be reproduced with GL on Vega.

It also improves performance because v_cvt_pkrtz_f16 is faster,
and because I guess the rounding mode behaviour is similar between
GL and VK, we can use it. About performance, it improves Talos
by +3/4% but I don't see any other impacts.

No CTS regressions on Polaris.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Reviewed-by: Dave Airlie <airlied at redhat.com>
(cherry picked from commit 5f81a43535e8512cef26ea3dcd1e3a489bd5a1bb)

---

 src/amd/common/ac_nir_to_llvm.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/src/amd/common/ac_nir_to_llvm.c b/src/amd/common/ac_nir_to_llvm.c
index d1d0475bde..f76534486c 100644
--- a/src/amd/common/ac_nir_to_llvm.c
+++ b/src/amd/common/ac_nir_to_llvm.c
@@ -1517,23 +1517,13 @@ static LLVMValueRef emit_bitfield_insert(struct ac_llvm_context *ctx,
 static LLVMValueRef emit_pack_half_2x16(struct ac_llvm_context *ctx,
 					LLVMValueRef src0)
 {
-	LLVMValueRef const16 = LLVMConstInt(ctx->i32, 16, false);
-	int i;
 	LLVMValueRef comp[2];
 
 	src0 = ac_to_float(ctx, src0);
 	comp[0] = LLVMBuildExtractElement(ctx->builder, src0, ctx->i32_0, "");
 	comp[1] = LLVMBuildExtractElement(ctx->builder, src0, ctx->i32_1, "");
-	for (i = 0; i < 2; i++) {
-		comp[i] = LLVMBuildFPTrunc(ctx->builder, comp[i], ctx->f16, "");
-		comp[i] = LLVMBuildBitCast(ctx->builder, comp[i], ctx->i16, "");
-		comp[i] = LLVMBuildZExt(ctx->builder, comp[i], ctx->i32, "");
-	}
-
-	comp[1] = LLVMBuildShl(ctx->builder, comp[1], const16, "");
-	comp[0] = LLVMBuildOr(ctx->builder, comp[0], comp[1], "");
 
-	return comp[0];
+	return ac_build_cvt_pkrtz_f16(ctx, comp);
 }
 
 static LLVMValueRef emit_unpack_half_2x16(struct ac_llvm_context *ctx,