glsl: Add new expressions for INTEL_shader_integer_functions2

v2: Re-write iadd64_saturate and isub64_saturate to avoid undefined
overflow behavior.  Also fix copy-and-paste bug in isub64_saturate.
Suggested by Caio.

v3: Avoid signed integer overflow for abs_sub(0, INT_MIN).  Noticed by
Caio.

v4: Alternate fix for signed integer overflow for abs_sub(0, INT_MIN).
I tried the previous methon in a small test program with -ftrapv, and it
failed.

Reviewed-by: Caio Marcelo de Oliveira Filho <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/767>

1 files changed, 36 insertions, 0 deletions

diff --git a/src/compiler/glsl/ir_constant_expression.cpp b/src/compiler/glsl/ir_constant_expression.cpp
index 5b1b5aa8eff..d7f0abe8304 100644
--- a/src/compiler/glsl/ir_constant_expression.cpp
+++ b/src/compiler/glsl/ir_constant_expression.cpp
@@ -416,6 +416,42 @@ unpack_half_1x16(uint16_t u)
    return _mesa_half_to_float(u);
 }
 
+static int32_t
+iadd_saturate(int32_t a, int32_t b)
+{
+   return CLAMP(int64_t(a) + int64_t(b), INT32_MIN, INT32_MAX);
+}
+
+static int64_t
+iadd64_saturate(int64_t a, int64_t b)
+{
+   if (a < 0 && b < INT64_MIN - a)
+      return INT64_MIN;
+
+   if (a > 0 && b > INT64_MAX - a)
+      return INT64_MAX;
+
+   return a + b;
+}
+
+static int32_t
+isub_saturate(int32_t a, int32_t b)
+{
+   return CLAMP(int64_t(a) - int64_t(b), INT32_MIN, INT32_MAX);
+}
+
+static int64_t
+isub64_saturate(int64_t a, int64_t b)
+{
+   if (b > 0 && a < INT64_MIN + b)
+      return INT64_MIN;
+
+   if (b < 0 && a > INT64_MAX + b)
+      return INT64_MAX;
+
+   return a - b;
+}
+
 /**
  * Get the constant that is ultimately referenced by an r-value, in a constant
  * expression evaluation context.