Mesa (master): vc4: Avoid false scheduling dependencies for LOAD_IMMs.

[Eric Anholt]

Module: Mesa
Branch: master
Commit: 51244859e368d9270a1f2f84aec6e97fbc1f5fac
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=51244859e368d9270a1f2f84aec6e97fbc1f5fac

Author: Eric Anholt <eric at anholt.net>
Date:   Wed Nov 30 14:00:28 2016 -0800

vc4: Avoid false scheduling dependencies for LOAD_IMMs.

Noticed in shaders with branching, where we ended up scheduling delay
slots near the start of a block for the uniforms reset setup.

total instructions in shared programs: 93970 -> 93951 (-0.02%)
instructions in affected programs:     3117 -> 3098 (-0.61%)

3DMMES performance +0.423087% +/- 0.133521% (n=9,10)

---

 src/gallium/drivers/vc4/vc4_qpu_schedule.c | 5 +++++
 src/gallium/drivers/vc4/vc4_qpu_validate.c | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/src/gallium/drivers/vc4/vc4_qpu_schedule.c b/src/gallium/drivers/vc4/vc4_qpu_schedule.c
index 878cdf9..4b2cb9d 100644
--- a/src/gallium/drivers/vc4/vc4_qpu_schedule.c
+++ b/src/gallium/drivers/vc4/vc4_qpu_schedule.c
@@ -477,6 +477,11 @@ reads_too_soon_after_write(struct choose_scoreboard *scoreboard, uint64_t inst)
         uint32_t raddr_a = QPU_GET_FIELD(inst, QPU_RADDR_A);
         uint32_t raddr_b = QPU_GET_FIELD(inst, QPU_RADDR_B);
         uint32_t sig = QPU_GET_FIELD(inst, QPU_SIG);
+
+        /* Full immediate loads don't read any registers. */
+        if (sig == QPU_SIG_LOAD_IMM)
+                return false;
+
         uint32_t src_muxes[] = {
                 QPU_GET_FIELD(inst, QPU_ADD_A),
                 QPU_GET_FIELD(inst, QPU_ADD_B),
diff --git a/src/gallium/drivers/vc4/vc4_qpu_validate.c b/src/gallium/drivers/vc4/vc4_qpu_validate.c
index f18ba03..08dd6e5 100644
--- a/src/gallium/drivers/vc4/vc4_qpu_validate.c
+++ b/src/gallium/drivers/vc4/vc4_qpu_validate.c
@@ -58,6 +58,10 @@ _reads_reg(uint64_t inst, uint32_t r, bool ignore_a, bool ignore_b)
         if (QPU_GET_FIELD(inst, QPU_SIG) == QPU_SIG_BRANCH)
                 return false;
 
+        /* Load immediates don't read any registers. */
+        if (QPU_GET_FIELD(inst, QPU_SIG) == QPU_SIG_LOAD_IMM)
+                return false;
+
         for (int i = 0; i < ARRAY_SIZE(src_regs); i++) {
                 if (!ignore_a &&
                     src_regs[i].mux == QPU_MUX_A &&