nv50/ir: always return 0 when trying to read thread id along unit dim

Many many many compute shaders only define a 1- or 2-dimensional block,
but then continue to use system values that take the full 3d into
account (like gl_LocalInvocationIndex, etc). So for the special case
that a dimension is exactly 1, we know that the thread id along that
axis will always be 0, so return it as such and allow constant folding
to fix things up.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Pierre Moreau <pierre.morrow@free.fr>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>

src/gallium/drivers/nouveau/codegen/nv50_ir.cpp

@@ -1179,7 +1179,11 @@ nv50_ir_init_prog_info(struct nv50_ir_prog_info *info)
       info->prop.gp.instanceCount = 1;
       info->prop.gp.maxVertices = 1;
    }
-   info->prop.cp.numThreads = 1;
+   if (info->type == PIPE_SHADER_COMPUTE) {
+      info->prop.cp.numThreads[0] =
+      info->prop.cp.numThreads[1] =
+      info->prop.cp.numThreads[2] = 1;
+   }
    info->io.pointSize = 0xff;
    info->io.instanceId = 0xff;
    info->io.vertexId = 0xff;

src/gallium/drivers/nouveau/codegen/nv50_ir_driver.h

@@ -152,7 +152,7 @@ struct nv50_ir_prog_info
          uint32_t inputOffset; /* base address for user args */
          uint32_t sharedOffset; /* reserved space in s[] */
          uint32_t gridInfoBase;  /* base address for NTID,NCTAID */
-         uint32_t numThreads; /* max number of threads */
+         uint16_t numThreads[3]; /* max number of threads */
       } cp;
    } prop;
 

src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp

@@ -1140,7 +1140,6 @@ bool Source::scanSource()
    }
 
    info->io.viewportId = -1;
-   info->prop.cp.numThreads = 1;
 
    info->immd.data = (uint32_t *)MALLOC(scan.immediate_count * 16);
    info->immd.type = (ubyte *)MALLOC(scan.immediate_count * sizeof(ubyte));
@@ -1243,9 +1242,13 @@ void Source::scanProperty(const struct tgsi_full_property *prop)
          info->prop.tp.outputPrim = PIPE_PRIM_TRIANGLES; /* anything but points */
       break;
    case TGSI_PROPERTY_CS_FIXED_BLOCK_WIDTH:
+      info->prop.cp.numThreads[0] = prop->u[0].Data;
+      break;
    case TGSI_PROPERTY_CS_FIXED_BLOCK_HEIGHT:
+      info->prop.cp.numThreads[1] = prop->u[0].Data;
+      break;
    case TGSI_PROPERTY_CS_FIXED_BLOCK_DEPTH:
-      info->prop.cp.numThreads *= prop->u[0].Data;
+      info->prop.cp.numThreads[2] = prop->u[0].Data;
       break;
    case TGSI_PROPERTY_NUM_CLIPDIST_ENABLED:
       info->io.clipDistances = prop->u[0].Data;
@@ -2034,6 +2037,9 @@ Converter::fetchSrc(tgsi::Instruction::SrcRegister src, int c, Value *ptr)
       return ld->getDef(0);
    case TGSI_FILE_SYSTEM_VALUE:
       assert(!ptr);
+      if (info->sv[idx].sn == TGSI_SEMANTIC_THREAD_ID &&
+          info->prop.cp.numThreads[swz] == 1)
+         return zero;
       ld = mkOp1(OP_RDSV, TYPE_U32, getSSA(), srcToSym(src, c));
       ld->perPatch = info->sv[idx].patch;
       return ld->getDef(0);

src/gallium/drivers/nouveau/codegen/nv50_ir_target.h

@@ -174,7 +174,9 @@ public:
    virtual void getBuiltinCode(const uint32_t **code, uint32_t *size) const = 0;
 
    virtual void parseDriverInfo(const struct nv50_ir_prog_info *info) {
-      threads = info->prop.cp.numThreads;
+      threads = info->prop.cp.numThreads[0] *
+         info->prop.cp.numThreads[1] *
+         info->prop.cp.numThreads[2];
       if (threads == 0)
          threads = info->target >= NVISA_GK104_CHIPSET ? 1024 : 512;
    }