radeonsi: Fix use of 1- or 2- component GL_DOUBLE vbo's.

With Mesa 18.1, commit be973ed21f6e, si_llvm_load_input_vs()
changed the number of source 32-bit wide dword components
used for fetching vertex attributes into the vertex shader
from a constant 4 to a variable num_channels number, depending
on input data format, with some special case handling for
input data formats like 64-Bit doubles.

In the case of a GL_DOUBLE input data format with one
or two components though, e.g, submitted via ...

a) glTexCoordPointer(1, GL_DOUBLE, 0, buffer);
b) glTexCoordPointer(2, GL_DOUBLE, 0, buffer);

... the input format would be SI_FIX_FETCH_RG_64_FLOAT,
but no special case handling was implemented for that
case, so in the default path the number of 32-bit
dwords would be set to the number of float input components
derived from info->input_usage_mask. This ends with corrupted
input to the vertex shader, because fetching a 64-bit double
from the vbo requires fetching two 32-bit dwords instead of 1,
and fetching a two double input requires 4 dword fetches
instead of 2, so in these cases the vertex shader receives
incomplete/truncated input data:

a) float v = gl_MultiTexCoord0.x;  -> v.x is corrupted.
b) vec2  v = gl_MultiTexCoord0.xy; -> v.x is assigned
   correctly, but v.y is corrupted.

This happens with the standard TGSI IR compiled shaders.
Under NIR with R600_DEBUG=nir, we got correct behavior
because the current radeonsi nir code always assigns
info->input_usage_mask = TGSI_WRITEMASK_XYZW, thereby
always fetches 4 dwords regardless of what the shader
actually needs.

Fix this by properly assigning 2 or 4 dword fetches for
one or two component GL_DOUBLE input.

Fixes: be973ed21f ("radeonsi: load the right number of
       components for VS inputs and TBOs")

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: mesa-stable@lists.freedesktop.org
Cc: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/drivers/radeonsi/si_shader.c

@@ -563,6 +563,14 @@ void si_llvm_load_input_vs(
 
 	/* Do multiple loads for special formats. */
 	switch (fix_fetch) {
+	case SI_FIX_FETCH_RG_64_FLOAT:
+		num_fetches = 1; /* 1 2-dword or 4-dword load */
+		fetch_stride = 0;
+		if (util_last_bit(info->input_usage_mask[input_index]) >= 2)
+			num_channels = 4; /* 2 doubles in 4 dwords */
+		else
+			num_channels = 2; /* 1 double in 2 dwords */
+		break;
 	case SI_FIX_FETCH_RGB_64_FLOAT:
 		num_fetches = 3; /* 3 2-dword loads */
 		fetch_stride = 8;