gallium: add PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT

This avoids a serious r600g bug leading to a GPU hang.
The chances this bug will get fixed are pretty low now.

I deeply regret listening to others and not pushing this patch, leaving
other users with a GPU-crashing driver. Yes, it should be fixed
in the compiler and it's ugly, but users couldn't care less about that.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=86720

Cc: 11.0 10.6 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Brian Paul <brianp@vmware.com>

16 files changed, 45 insertions, 1 deletions

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_limits.h b/src/gallium/auxiliary/gallivm/lp_bld_limits.h
index 571c615..ad64ae0 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_limits.h
+++ b/src/gallium/auxiliary/gallivm/lp_bld_limits.h
@@ -137,6 +137,8 @@ gallivm_get_shader_param(enum pipe_shader_cap param)
    case PIPE_SHADER_CAP_TGSI_DFRACEXP_DLDEXP_SUPPORTED:
    case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
       return 0;
+   case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+      return 32;
    }
    /* if we get here, we missed a shader cap above (and should have seen
     * a compiler warning.)
diff --git a/src/gallium/auxiliary/tgsi/tgsi_exec.h b/src/gallium/auxiliary/tgsi/tgsi_exec.h
index a371aa9..f86adce 100644
--- a/src/gallium/auxiliary/tgsi/tgsi_exec.h
+++ b/src/gallium/auxiliary/tgsi/tgsi_exec.h
@@ -474,6 +474,8 @@ tgsi_exec_get_shader_param(enum pipe_shader_cap param)
    case PIPE_SHADER_CAP_TGSI_DROUND_SUPPORTED:
    case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
       return 0;
+   case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+      return 32;
    }
    /* if we get here, we missed a shader cap above (and should have seen
     * a compiler warning.)
diff --git a/src/gallium/docs/source/screen.rst b/src/gallium/docs/source/screen.rst
index 72f7596..151afb2 100644
--- a/src/gallium/docs/source/screen.rst
+++ b/src/gallium/docs/source/screen.rst
@@ -367,6 +367,10 @@ to be 0.
   are supported.
 * ``PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE``: Whether the driver doesn't
   ignore tgsi_declaration_range::Last for shader inputs and outputs.
+* ``PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT``: This is the maximum number
+  of iterations that loops are allowed to have to be unrolled. It is only
+  a hint to state trackers. Whether any loops will be unrolled is not
+  guaranteed.
 
 
 .. _pipe_compute_cap:
diff --git a/src/gallium/drivers/freedreno/freedreno_screen.c b/src/gallium/drivers/freedreno/freedreno_screen.c
index f85e458..50d140f 100644
--- a/src/gallium/drivers/freedreno/freedreno_screen.c
+++ b/src/gallium/drivers/freedreno/freedreno_screen.c
@@ -412,6 +412,8 @@ fd_screen_get_shader_param(struct pipe_screen *pscreen, unsigned shader,
 		return 16;
 	case PIPE_SHADER_CAP_PREFERRED_IR:
 		return PIPE_SHADER_IR_TGSI;
+	case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+		return 32;
 	}
 	debug_printf("unknown shader param %d\n", param);
 	return 0;
diff --git a/src/gallium/drivers/i915/i915_screen.c b/src/gallium/drivers/i915/i915_screen.c
index c91408d..5812af6 100644
--- a/src/gallium/drivers/i915/i915_screen.c
+++ b/src/gallium/drivers/i915/i915_screen.c
@@ -167,6 +167,8 @@ i915_get_shader_param(struct pipe_screen *screen, unsigned shader, enum pipe_sha
       case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
       case PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE:
          return 0;
+      case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+         return 32;
       default:
          debug_printf("%s: Unknown cap %u.\n", __FUNCTION__, cap);
          return 0;
diff --git a/src/gallium/drivers/ilo/ilo_screen.c b/src/gallium/drivers/ilo/ilo_screen.c
index acf688f..e1a7dc5 100644
--- a/src/gallium/drivers/ilo/ilo_screen.c
+++ b/src/gallium/drivers/ilo/ilo_screen.c
@@ -138,6 +138,8 @@ ilo_get_shader_param(struct pipe_screen *screen, unsigned shader,
       return PIPE_SHADER_IR_TGSI;
    case PIPE_SHADER_CAP_TGSI_SQRT_SUPPORTED:
       return 1;
+   case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+      return 32;
 
    default:
       return 0;
diff --git a/src/gallium/drivers/nouveau/nv30/nv30_screen.c b/src/gallium/drivers/nouveau/nv30/nv30_screen.c
index d4cf143..0330164 100644
--- a/src/gallium/drivers/nouveau/nv30/nv30_screen.c
+++ b/src/gallium/drivers/nouveau/nv30/nv30_screen.c
@@ -264,6 +264,8 @@ nv30_screen_get_shader_param(struct pipe_screen *pscreen, unsigned shader,
       case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
       case PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE:
          return 0;
+      case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+         return 32;
       default:
          debug_printf("unknown vertex shader param %d\n", param);
          return 0;
@@ -305,6 +307,8 @@ nv30_screen_get_shader_param(struct pipe_screen *pscreen, unsigned shader,
       case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
       case PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE:
          return 0;
+      case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+         return 32;
       default:
          debug_printf("unknown fragment shader param %d\n", param);
          return 0;
diff --git a/src/gallium/drivers/nouveau/nv50/nv50_screen.c b/src/gallium/drivers/nouveau/nv50/nv50_screen.c
index a4431f2..ec51d00 100644
--- a/src/gallium/drivers/nouveau/nv50/nv50_screen.c
+++ b/src/gallium/drivers/nouveau/nv50/nv50_screen.c
@@ -300,6 +300,8 @@ nv50_screen_get_shader_param(struct pipe_screen *pscreen, unsigned shader,
    case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
    case PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE:
       return 0;
+   case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+      return 32;
    default:
       NOUVEAU_ERR("unknown PIPE_SHADER_CAP %d\n", param);
       return 0;
diff --git a/src/gallium/drivers/nouveau/nvc0/nvc0_screen.c b/src/gallium/drivers/nouveau/nvc0/nvc0_screen.c
index d34c8a2..af8e5f7 100644
--- a/src/gallium/drivers/nouveau/nvc0/nvc0_screen.c
+++ b/src/gallium/drivers/nouveau/nvc0/nvc0_screen.c
@@ -313,6 +313,8 @@ nvc0_screen_get_shader_param(struct pipe_screen *pscreen, unsigned shader,
       return 16; /* would be 32 in linked (OpenGL-style) mode */
    case PIPE_SHADER_CAP_MAX_SAMPLER_VIEWS:
       return 16; /* XXX not sure if more are really safe */
+   case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+      return 32;
    default:
       NOUVEAU_ERR("unknown PIPE_SHADER_CAP %d\n", param);
       return 0;
diff --git a/src/gallium/drivers/r300/r300_screen.c b/src/gallium/drivers/r300/r300_screen.c
index c1c522b..a576abd 100644
--- a/src/gallium/drivers/r300/r300_screen.c
+++ b/src/gallium/drivers/r300/r300_screen.c
@@ -303,6 +303,8 @@ static int r300_get_shader_param(struct pipe_screen *pscreen, unsigned shader, e
         case PIPE_SHADER_CAP_TGSI_DFRACEXP_DLDEXP_SUPPORTED:
         case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
             return 0;
+        case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+            return 32;
         case PIPE_SHADER_CAP_PREFERRED_IR:
             return PIPE_SHADER_IR_TGSI;
         }
@@ -359,6 +361,8 @@ static int r300_get_shader_param(struct pipe_screen *pscreen, unsigned shader, e
         case PIPE_SHADER_CAP_TGSI_DFRACEXP_DLDEXP_SUPPORTED:
         case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
             return 0;
+        case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+            return 32;
         case PIPE_SHADER_CAP_PREFERRED_IR:
             return PIPE_SHADER_IR_TGSI;
         }
diff --git a/src/gallium/drivers/r600/r600_pipe.c b/src/gallium/drivers/r600/r600_pipe.c
index 75de553..9a97de9 100644
--- a/src/gallium/drivers/r600/r600_pipe.c
+++ b/src/gallium/drivers/r600/r600_pipe.c
@@ -511,6 +511,12 @@ static int r600_get_shader_param(struct pipe_screen* pscreen, unsigned shader, e
 	case PIPE_SHADER_CAP_TGSI_DFRACEXP_DLDEXP_SUPPORTED:
 	case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
 		return 0;
+	case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+		/* due to a bug in the shader compiler, some loops hang
+		 * if they are not unrolled, see:
+		 *    https://bugs.freedesktop.org/show_bug.cgi?id=86720
+		 */
+		return 255;
 	}
 	return 0;
 }
diff --git a/src/gallium/drivers/radeonsi/si_pipe.c b/src/gallium/drivers/radeonsi/si_pipe.c
index c084f03..5f910c9 100644
--- a/src/gallium/drivers/radeonsi/si_pipe.c
+++ b/src/gallium/drivers/radeonsi/si_pipe.c
@@ -508,6 +508,8 @@ static int si_get_shader_param(struct pipe_screen* pscreen, unsigned shader, enu
 	case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
 	case PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE:
 		return 1;
+	case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+		return 32;
 	}
 	return 0;
 }
diff --git a/src/gallium/drivers/svga/svga_screen.c b/src/gallium/drivers/svga/svga_screen.c
index 9bf661f..17b042e 100644
--- a/src/gallium/drivers/svga/svga_screen.c
+++ b/src/gallium/drivers/svga/svga_screen.c
@@ -456,6 +456,8 @@ vgpu9_get_shader_param(struct pipe_screen *screen, unsigned shader,
       case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
       case PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE:
          return 0;
+      case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+         return 32;
       }
       /* If we get here, we failed to handle a cap above */
       debug_printf("Unexpected fragment shader query %u\n", param);
@@ -512,6 +514,8 @@ vgpu9_get_shader_param(struct pipe_screen *screen, unsigned shader,
       case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
       case PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE:
          return 0;
+      case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+         return 32;
       }
       /* If we get here, we failed to handle a cap above */
       debug_printf("Unexpected vertex shader query %u\n", param);
diff --git a/src/gallium/drivers/vc4/vc4_screen.c b/src/gallium/drivers/vc4/vc4_screen.c
index 3b12464..774ec09 100644
--- a/src/gallium/drivers/vc4/vc4_screen.c
+++ b/src/gallium/drivers/vc4/vc4_screen.c
@@ -337,6 +337,8 @@ vc4_screen_get_shader_param(struct pipe_screen *pscreen, unsigned shader,
                 return VC4_MAX_TEXTURE_SAMPLERS;
         case PIPE_SHADER_CAP_PREFERRED_IR:
                 return PIPE_SHADER_IR_TGSI;
+	case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
+		return 32;
         default:
                 fprintf(stderr, "unknown shader param %d\n", param);
                 return 0;
diff --git a/src/gallium/include/pipe/p_defines.h b/src/gallium/include/pipe/p_defines.h
index 3a1265d..1ad545a 100644
--- a/src/gallium/include/pipe/p_defines.h
+++ b/src/gallium/include/pipe/p_defines.h
@@ -697,7 +697,8 @@ enum pipe_shader_cap
    PIPE_SHADER_CAP_TGSI_DROUND_SUPPORTED, /* all rounding modes */
    PIPE_SHADER_CAP_TGSI_DFRACEXP_DLDEXP_SUPPORTED,
    PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED,
-   PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE
+   PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE,
+   PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT,
 };
 
 /**
diff --git a/src/mesa/state_tracker/st_extensions.c b/src/mesa/state_tracker/st_extensions.c
index e290292..d4724b4 100644
--- a/src/mesa/state_tracker/st_extensions.c
+++ b/src/mesa/state_tracker/st_extensions.c
@@ -249,6 +249,9 @@ void st_init_limits(struct pipe_screen *screen,
 
       if (options->EmitNoLoops)
          options->MaxUnrollIterations = MIN2(screen->get_shader_param(screen, sh, PIPE_SHADER_CAP_MAX_INSTRUCTIONS), 65536);
+      else
+         options->MaxUnrollIterations = screen->get_shader_param(screen, sh,
+                                      PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT);
 
       options->LowerClipDistance = true;
    }