i965: Accurately bail on SIMD16 compiles.

Ideally, we'd like to never even attempt the SIMD16 compile if we could
know ahead of time that it won't succeed---it's purely a waste of time.
This is especially important for state-based recompiles, which happen at
draw time.

The fragment shader compiler has a number of checks like:

   if (dispatch_width == 16)
      fail("...some reason...");

This patch introduces a new no16() function which replaces the above
pattern.  In the SIMD8 compile, it sets a "SIMD16 will never work" flag.
Then, brw_wm_fs_emit can check that flag, skip the SIMD16 compile, and
issue a helpful performance warning if INTEL_DEBUG=perf is set.  (In
SIMD16 mode, no16() calls fail(), for safety's sake.)

The great part is that this is not a heuristic---if the flag is set, we
know with 100% certainty that the SIMD16 compile would fail.  (It might
fail anyway if we run out of registers, but it's always worth trying.)

v2: Fix missing va_end in early-return case (caught by Ilia Mirkin).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz> [v1]
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com> [v1]
Reviewed-by: Eric Anholt <eric@anholt.net>

3 files changed, 82 insertions, 34 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 1f85901..1b32d63 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -647,9 +647,8 @@ fs_visitor::emit_shader_time_write(enum shader_time_shader_type type,
 }
 
 void
-fs_visitor::fail(const char *format, ...)
+fs_visitor::vfail(const char *format, va_list va)
 {
-   va_list va;
    char *msg;
 
    if (failed)
@@ -657,9 +656,7 @@ fs_visitor::fail(const char *format, ...)
 
    failed = true;
 
-   va_start(va, format);
    msg = ralloc_vasprintf(mem_ctx, format, va);
-   va_end(va);
    msg = ralloc_asprintf(mem_ctx, "FS compile failed: %s\n", msg);
 
    this->fail_msg = msg;
@@ -669,6 +666,48 @@ fs_visitor::fail(const char *format, ...)
    }
 }
 
+void
+fs_visitor::fail(const char *format, ...)
+{
+   va_list va;
+
+   va_start(va, format);
+   vfail(format, va);
+   va_end(va);
+}
+
+/**
+ * Mark this program as impossible to compile in SIMD16 mode.
+ *
+ * During the SIMD8 compile (which happens first), we can detect and flag
+ * things that are unsupported in SIMD16 mode, so the compiler can skip
+ * the SIMD16 compile altogether.
+ *
+ * During a SIMD16 compile (if one happens anyway), this just calls fail().
+ */
+void
+fs_visitor::no16(const char *format, ...)
+{
+   va_list va;
+
+   va_start(va, format);
+
+   if (dispatch_width == 16) {
+      vfail(format, va);
+   } else {
+      simd16_unsupported = true;
+
+      if (INTEL_DEBUG & DEBUG_PERF) {
+         if (no16_msg)
+            ralloc_vasprintf_append(&no16_msg, format, va);
+         else
+            no16_msg = ralloc_vasprintf(mem_ctx, format, va);
+      }
+   }
+
+   va_end(va);
+}
+
 fs_inst *
 fs_visitor::emit(enum opcode opcode)
 {
@@ -1356,8 +1395,8 @@ fs_visitor::emit_math(enum opcode opcode, fs_reg dst, fs_reg src0, fs_reg src1)
    switch (opcode) {
    case SHADER_OPCODE_INT_QUOTIENT:
    case SHADER_OPCODE_INT_REMAINDER:
-      if (brw->gen >= 7 && dispatch_width == 16)
-	 fail("SIMD16 INTDIV unsupported\n");
+      if (brw->gen >= 7)
+	 no16("SIMD16 INTDIV unsupported\n");
       break;
    case SHADER_OPCODE_POW:
       break;
@@ -3505,13 +3544,18 @@ brw_wm_fs_emit(struct brw_context *brw, struct brw_wm_compile *c,
    exec_list *simd16_instructions = NULL;
    fs_visitor v2(brw, c, prog, fp, 16);
    if (brw->gen >= 5 && likely(!(INTEL_DEBUG & DEBUG_NO16))) {
-      /* Try a SIMD16 compile */
-      v2.import_uniforms(&v);
-      if (!v2.run()) {
-         perf_debug("SIMD16 shader failed to compile, falling back to "
-                    "SIMD8 at a 10-20%% performance cost: %s", v2.fail_msg);
+      if (!v.simd16_unsupported) {
+         /* Try a SIMD16 compile */
+         v2.import_uniforms(&v);
+         if (!v2.run()) {
+            perf_debug("SIMD16 shader failed to compile, falling back to "
+                       "SIMD8 at a 10-20%% performance cost: %s", v2.fail_msg);
+         } else {
+            simd16_instructions = &v2.instructions;
+         }
       } else {
-         simd16_instructions = &v2.instructions;
+         perf_debug("SIMD16 shader unsupported, falling back to "
+                    "SIMD8 at a 10-20%% performance cost: %s", v.no16_msg);
       }
    }
 
diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
index 9de1f3a..0d064f6 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_fs.h
@@ -381,7 +381,9 @@ public:
    void insert_gen4_send_dependency_workarounds();
    void insert_gen4_pre_send_dependency_workarounds(fs_inst *inst);
    void insert_gen4_post_send_dependency_workarounds(fs_inst *inst);
+   void vfail(const char *msg, va_list args);
    void fail(const char *msg, ...);
+   void no16(const char *msg, ...);
    void lower_uniform_pull_constant_loads();
 
    void push_force_uncompressed();
@@ -541,6 +543,8 @@ public:
 
    bool failed;
    char *fail_msg;
+   bool simd16_unsupported;
+   char *no16_msg;
 
    /* Result of last visit() method. */
    fs_reg result;
diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index cd90e23..a832268 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -462,8 +462,8 @@ fs_visitor::visit(ir_expression *ir)
 	  * FINISHME: Emit just the MUL if we know an operand is small
 	  * enough.
 	  */
-	 if (brw->gen >= 7 && dispatch_width == 16)
-	    fail("SIMD16 explicit accumulator operands unsupported\n");
+	 if (brw->gen >= 7)
+	    no16("SIMD16 explicit accumulator operands unsupported\n");
 
 	 struct brw_reg acc = retype(brw_acc_reg(), this->result.type);
 
@@ -475,8 +475,8 @@ fs_visitor::visit(ir_expression *ir)
       }
       break;
    case ir_binop_imul_high: {
-      if (brw->gen >= 7 && dispatch_width == 16)
-         fail("SIMD16 explicit accumulator operands unsupported\n");
+      if (brw->gen >= 7)
+         no16("SIMD16 explicit accumulator operands unsupported\n");
 
       struct brw_reg acc = retype(brw_acc_reg(), this->result.type);
 
@@ -490,8 +490,8 @@ fs_visitor::visit(ir_expression *ir)
       emit_math(SHADER_OPCODE_INT_QUOTIENT, this->result, op[0], op[1]);
       break;
    case ir_binop_carry: {
-      if (brw->gen >= 7 && dispatch_width == 16)
-         fail("SIMD16 explicit accumulator operands unsupported\n");
+      if (brw->gen >= 7)
+         no16("SIMD16 explicit accumulator operands unsupported\n");
 
       struct brw_reg acc = retype(brw_acc_reg(), BRW_REGISTER_TYPE_UD);
 
@@ -500,8 +500,8 @@ fs_visitor::visit(ir_expression *ir)
       break;
    }
    case ir_binop_borrow: {
-      if (brw->gen >= 7 && dispatch_width == 16)
-         fail("SIMD16 explicit accumulator operands unsupported\n");
+      if (brw->gen >= 7)
+         no16("SIMD16 explicit accumulator operands unsupported\n");
 
       struct brw_reg acc = retype(brw_acc_reg(), BRW_REGISTER_TYPE_UD);
 
@@ -1290,8 +1290,7 @@ fs_visitor::emit_texture_gen7(ir_texture *ir, fs_reg dst, fs_reg coordinate,
       next.reg_offset++;
       break;
    case ir_txd: {
-      if (dispatch_width == 16)
-	 fail("Gen7 does not support sample_d/sample_d_c in SIMD16 mode.");
+      no16("Gen7 does not support sample_d/sample_d_c in SIMD16 mode.");
 
       /* Load dPdx and the coordinate together:
        * [hdr], [ref], x, dPdx.x, dPdy.x, y, dPdx.y, dPdy.y, z, dPdx.z, dPdy.z
@@ -1364,8 +1363,8 @@ fs_visitor::emit_texture_gen7(ir_texture *ir, fs_reg dst, fs_reg coordinate,
       break;
    case ir_tg4:
       if (has_nonconstant_offset) {
-         if (ir->shadow_comparitor && dispatch_width == 16)
-            fail("Gen7 does not support gather4_po_c in SIMD16 mode.");
+         if (ir->shadow_comparitor)
+            no16("Gen7 does not support gather4_po_c in SIMD16 mode.");
 
          /* More crazy intermixing */
          ir->offset->accept(this);
@@ -1464,8 +1463,8 @@ fs_visitor::rescale_texcoord(ir_texture *ir, fs_reg coordinate,
 	 0
       };
 
+      no16("rectangle scale uniform setup not supported on SIMD16\n");
       if (dispatch_width == 16) {
-	 fail("rectangle scale uniform setup not supported on SIMD16\n");
 	 return coordinate;
       }
 
@@ -2183,8 +2182,8 @@ fs_visitor::try_replace_with_sel()
 void
 fs_visitor::visit(ir_if *ir)
 {
-   if (brw->gen < 6 && dispatch_width == 16) {
-      fail("Can't support (non-uniform) control flow on SIMD16\n");
+   if (brw->gen < 6) {
+      no16("Can't support (non-uniform) control flow on SIMD16\n");
    }
 
    /* Don't point the annotation at the if statement, because then it plus
@@ -2226,8 +2225,8 @@ fs_visitor::visit(ir_if *ir)
 void
 fs_visitor::visit(ir_loop *ir)
 {
-   if (brw->gen < 6 && dispatch_width == 16) {
-      fail("Can't support (non-uniform) control flow on SIMD16\n");
+   if (brw->gen < 6) {
+      no16("Can't support (non-uniform) control flow on SIMD16\n");
    }
 
    this->base_ir = NULL;
@@ -2725,9 +2724,10 @@ fs_visitor::emit_fb_writes()
    bool do_dual_src = this->dual_src_output.file != BAD_FILE;
    bool src0_alpha_to_render_target = false;
 
-   if (dispatch_width == 16 && do_dual_src) {
-      fail("GL_ARB_blend_func_extended not yet supported in SIMD16.");
-      do_dual_src = false;
+   if (do_dual_src) {
+      no16("GL_ARB_blend_func_extended not yet supported in SIMD16.");
+      if (dispatch_width == 16)
+         do_dual_src = false;
    }
 
    /* From the Sandy Bridge PRM, volume 4, page 198:
@@ -2778,13 +2778,13 @@ fs_visitor::emit_fb_writes()
       nr += reg_width;
 
    if (c->source_depth_to_render_target) {
-      if (brw->gen == 6 && dispatch_width == 16) {
+      if (brw->gen == 6) {
 	 /* For outputting oDepth on gen6, SIMD8 writes have to be
 	  * used.  This would require SIMD8 moves of each half to
 	  * message regs, kind of like pre-gen5 SIMD16 FB writes.
 	  * Just bail on doing so for now.
 	  */
-	 fail("Missing support for simd16 depth writes on gen6\n");
+	 no16("Missing support for simd16 depth writes on gen6\n");
       }
 
       if (prog->OutputsWritten & BITFIELD64_BIT(FRAG_RESULT_DEPTH)) {