Mesa (master): nir_opcodes.py: Saturate to expression that doesn't overflow

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Module: Mesa
Branch: master
Commit: 41593f3c3711cd61156d91ad12bb8aabf91a9556
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=41593f3c3711cd61156d91ad12bb8aabf91a9556

Author: Kristian H. Kristensen <hoegsberg at google.com>
Date:   Thu Apr 18 11:23:13 2019 -0700

nir_opcodes.py: Saturate to expression that doesn't overflow

Compiler warns about overflow when assigning UINT64_MAX to something
smaller than a uin64_t:

src/compiler/nir/nir_constant_expressions.c:16909:50: warning: implicit conversion from 'unsigned long long' to 'uint1_t' (aka 'unsigned char') changes value from 18446744073709551615 to 255 [-Wconstant-conversion]
            uint1_t dst = (src0 + src1) < src0 ? UINT64_MAX : (src0 + src1);
                    ~~~                          ^~~~~~~~~~

Shift UINT64_MAX down to the appropriate maximum value for the type
being assigned to.

Signed-off-by: Kristian H. Kristensen <hoegsberg at google.com>
Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>

---

 src/compiler/nir/nir_constant_expressions.py | 2 ++
 src/compiler/nir/nir_opcodes.py              | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/compiler/nir/nir_constant_expressions.py b/src/compiler/nir/nir_constant_expressions.py
index 0f89e90d7b7..f26fd0a3ea2 100644
--- a/src/compiler/nir/nir_constant_expressions.py
+++ b/src/compiler/nir/nir_constant_expressions.py
@@ -66,6 +66,8 @@ template = """\
 #include "util/bigmath.h"
 #include "nir_constant_expressions.h"
 
+#define MAX_UINT_FOR_SIZE(bits) (UINT64_MAX >> (64 - (bits)))
+
 /**
  * Evaluate one component of packSnorm4x8.
  */
diff --git a/src/compiler/nir/nir_opcodes.py b/src/compiler/nir/nir_opcodes.py
index 0f56dd9596c..d35d820aa5b 100644
--- a/src/compiler/nir/nir_opcodes.py
+++ b/src/compiler/nir/nir_opcodes.py
@@ -488,7 +488,7 @@ binop("iadd_sat", tint, commutative + associative, """
          (src0 < src0 + src1 ? (1ull << (bit_size - 1))     : src0 + src1)
 """)
 binop("uadd_sat", tuint, commutative,
-      "(src0 + src1) < src0 ? UINT64_MAX : (src0 + src1)")
+      "(src0 + src1) < src0 ? MAX_UINT_FOR_SIZE(sizeof(src0) * 8) : (src0 + src1)")
 binop("isub_sat", tint, "", """
       src1 < 0 ?
          (src0 - src1 < src0 ? (1ull << (bit_size - 1)) - 1 : src0 - src1) :