Mesa (master): panfrost/midgard: Safety check immediate precision degradations

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Module: Mesa
Branch: master
Commit: 3978614d8818ece6e1e252490f4bcab670db806a
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=3978614d8818ece6e1e252490f4bcab670db806a

Author: Alyssa Rosenzweig <alyssa at rosenzweig.io>
Date:   Sun Apr 28 15:46:47 2019 +0000

panfrost/midgard: Safety check immediate precision degradations

Signed-off-by: Alyssa Rosenzweig <alyssa at rosenzweig.io>

---

 src/gallium/drivers/panfrost/midgard/midgard_compile.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/gallium/drivers/panfrost/midgard/midgard_compile.c b/src/gallium/drivers/panfrost/midgard/midgard_compile.c
index 2b97bbc86f6..348ec861404 100644
--- a/src/gallium/drivers/panfrost/midgard/midgard_compile.c
+++ b/src/gallium/drivers/panfrost/midgard/midgard_compile.c
@@ -3047,7 +3047,20 @@ embedded_to_inline_constant(compiler_context *ctx)
                                 if (scaled_constant != iconstants[component])
                                         continue;
                         } else {
-                                scaled_constant = _mesa_float_to_half((float) ins->constants[component]);
+                                float original = (float) ins->constants[component];
+                                scaled_constant = _mesa_float_to_half(original);
+
+                                /* Check for loss of precision. If this is
+                                 * mediump, we don't care, but for a highp
+                                 * shader, we need to pay attention. NIR
+                                 * doesn't yet tell us which mode we're in!
+                                 * Practically this prevents most constants
+                                 * from being inlined, sadly. */
+
+                                float fp32 = _mesa_half_to_float(scaled_constant);
+
+                                if (fp32 != original)
+                                        continue;
                         }
 
                         /* We don't know how to handle these with a constant */