[naga wgsl-out] Improve representation of minimum int64 literal

#7424 fixed a bug where the representation of the minimum int64 literal
generated by naga was invalid WGSL. It changed us from expressing it as
`-9223372036854775808` which was invalid, to `-9223372036854775807li -
1li`.

This is valid WGSL. However, as the values are concrete i64 types if the
shader is parsed again by naga the expression does not get const
evaluated away, leading to suboptimal code generated by the
backends. This patch makes us perform the subtraction using abstract
integers before casting to i64, solving this problem.

Additionally the input WGSL test is updated to use the same construct.

Author: jamienicol

naga/src/back/wgsl/writer.rs

@@ -1147,12 +1147,12 @@ impl<W: Write> Writer<W> {
                 crate::Literal::Bool(value) => write!(self.out, "{value}")?,
                 crate::Literal::F64(value) => write!(self.out, "{value:?}lf")?,
                 crate::Literal::I64(value) => {
-                    // `-9223372036854775808li` is not valid WGSL. Nor can we use the AbstractInt
-                    // trick above, as AbstractInt also cannot represent `9223372036854775808`.
-                    // The most negative `i64` value can only be expressed in WGSL using
-                    // subtracting 1 from the second most negative value.
+                    // `-9223372036854775808li` is not valid WGSL. Nor can we simply use the
+                    // AbstractInt trick above, as AbstractInt also cannot represent
+                    // `9223372036854775808`. Instead construct the second most negative
+                    // AbstractInt, subtract one from it, then cast to i64.
                     if value == i64::MIN {
-                        write!(self.out, "{}li - 1li", value + 1)?;
+                        write!(self.out, "i64({} - 1)", value + 1)?;
                     } else {
                         write!(self.out, "{value}li")?;
                     }

naga/tests/in/wgsl/int64.wgsl

@@ -56,7 +56,7 @@ fn int64_function(x: i64) -> i64 {
    val += bitcast<vec3<i64>>(input_uniform.val_u64_3).z;
    val += bitcast<vec4<i64>>(input_uniform.val_u64_4).w;
    // Most negative i64
-   val += -9223372036854775807li - 1li;
+   val += i64(-9223372036854775807 - 1);
 
    // Reading/writing to a uniform/storage buffer
    output.val_i64 = input_uniform.val_i64 + input_storage.val_i64;

naga/tests/out/hlsl/int64.hlsl

@@ -95,51 +95,51 @@ int64_t int64_function(int64_t x)
     uint64_t4 _e71 = input_uniform.val_u64_4_;
     int64_t _e74 = val;
     val = (_e74 + _e71.w);
-    int64_t _e79 = val;
-    val = (_e79 + (-9223372036854775807L - 1L));
-    int64_t _e85 = input_uniform.val_i64_;
-    int64_t _e88 = input_storage.Load<int64_t>(128);
-    output.Store(128, (_e85 + _e88));
-    int64_t2 _e94 = input_uniform.val_i64_2_;
-    int64_t2 _e97 = input_storage.Load<int64_t2>(144);
-    output.Store(144, (_e94 + _e97));
-    int64_t3 _e103 = input_uniform.val_i64_3_;
-    int64_t3 _e106 = input_storage.Load<int64_t3>(160);
-    output.Store(160, (_e103 + _e106));
-    int64_t4 _e112 = input_uniform.val_i64_4_;
-    int64_t4 _e115 = input_storage.Load<int64_t4>(192);
-    output.Store(192, (_e112 + _e115));
-    int64_t _e121[2] = Constructarray2_int64_t_(input_arrays.Load<int64_t>(16+0), input_arrays.Load<int64_t>(16+8));
+    int64_t _e77 = val;
+    val = (_e77 + -9223372036854775808L);
+    int64_t _e83 = input_uniform.val_i64_;
+    int64_t _e86 = input_storage.Load<int64_t>(128);
+    output.Store(128, (_e83 + _e86));
+    int64_t2 _e92 = input_uniform.val_i64_2_;
+    int64_t2 _e95 = input_storage.Load<int64_t2>(144);
+    output.Store(144, (_e92 + _e95));
+    int64_t3 _e101 = input_uniform.val_i64_3_;
+    int64_t3 _e104 = input_storage.Load<int64_t3>(160);
+    output.Store(160, (_e101 + _e104));
+    int64_t4 _e110 = input_uniform.val_i64_4_;
+    int64_t4 _e113 = input_storage.Load<int64_t4>(192);
+    output.Store(192, (_e110 + _e113));
+    int64_t _e119[2] = Constructarray2_int64_t_(input_arrays.Load<int64_t>(16+0), input_arrays.Load<int64_t>(16+8));
     {
-        int64_t _value2[2] = _e121;
+        int64_t _value2[2] = _e119;
         output_arrays.Store(16+0, _value2[0]);
         output_arrays.Store(16+8, _value2[1]);
     }
+    int64_t _e120 = val;
     int64_t _e122 = val;
+    val = (_e122 + abs(_e120));
     int64_t _e124 = val;
-    val = (_e124 + abs(_e122));
+    int64_t _e125 = val;
     int64_t _e126 = val;
-    int64_t _e127 = val;
     int64_t _e128 = val;
+    val = (_e128 + clamp(_e124, _e125, _e126));
     int64_t _e130 = val;
-    val = (_e130 + clamp(_e126, _e127, _e128));
     int64_t _e132 = val;
-    int64_t _e134 = val;
+    int64_t _e135 = val;
+    val = (_e135 + dot((_e130).xx, (_e132).xx));
     int64_t _e137 = val;
-    val = (_e137 + dot((_e132).xx, (_e134).xx));
-    int64_t _e139 = val;
+    int64_t _e138 = val;
     int64_t _e140 = val;
+    val = (_e140 + max(_e137, _e138));
     int64_t _e142 = val;
-    val = (_e142 + max(_e139, _e140));
-    int64_t _e144 = val;
+    int64_t _e143 = val;
     int64_t _e145 = val;
+    val = (_e145 + min(_e142, _e143));
     int64_t _e147 = val;
-    val = (_e147 + min(_e144, _e145));
     int64_t _e149 = val;
+    val = (_e149 + sign(_e147));
     int64_t _e151 = val;
-    val = (_e151 + sign(_e149));
-    int64_t _e153 = val;
-    return _e153;
+    return _e151;
 }
 
 typedef uint64_t ret_Constructarray2_uint64_t_[2];

naga/tests/out/msl/int64.msl

@@ -79,49 +79,49 @@ long int64_function(
     metal::ulong4 _e71 = input_uniform.val_u64_4_;
     long _e74 = val;
     val = as_type<long>(as_type<ulong>(_e74) + as_type<ulong>(as_type<metal::long4>(_e71).w));
-    long _e79 = val;
-    val = as_type<long>(as_type<ulong>(_e79) + as_type<ulong>(as_type<long>(as_type<ulong>(-9223372036854775807L) - as_type<ulong>(1L))));
-    long _e85 = input_uniform.val_i64_;
-    long _e88 = input_storage.val_i64_;
-    output.val_i64_ = as_type<long>(as_type<ulong>(_e85) + as_type<ulong>(_e88));
-    metal::long2 _e94 = input_uniform.val_i64_2_;
-    metal::long2 _e97 = input_storage.val_i64_2_;
-    output.val_i64_2_ = as_type<metal::long2>(as_type<metal::ulong2>(_e94) + as_type<metal::ulong2>(_e97));
-    metal::long3 _e103 = input_uniform.val_i64_3_;
-    metal::long3 _e106 = input_storage.val_i64_3_;
-    output.val_i64_3_ = as_type<metal::long3>(as_type<metal::ulong3>(_e103) + as_type<metal::ulong3>(_e106));
-    metal::long4 _e112 = input_uniform.val_i64_4_;
-    metal::long4 _e115 = input_storage.val_i64_4_;
-    output.val_i64_4_ = as_type<metal::long4>(as_type<metal::ulong4>(_e112) + as_type<metal::ulong4>(_e115));
-    type_12 _e121 = input_arrays.val_i64_array_2_;
-    output_arrays.val_i64_array_2_ = _e121;
+    long _e77 = val;
+    val = as_type<long>(as_type<ulong>(_e77) + as_type<ulong>(-9223372036854775808L));
+    long _e83 = input_uniform.val_i64_;
+    long _e86 = input_storage.val_i64_;
+    output.val_i64_ = as_type<long>(as_type<ulong>(_e83) + as_type<ulong>(_e86));
+    metal::long2 _e92 = input_uniform.val_i64_2_;
+    metal::long2 _e95 = input_storage.val_i64_2_;
+    output.val_i64_2_ = as_type<metal::long2>(as_type<metal::ulong2>(_e92) + as_type<metal::ulong2>(_e95));
+    metal::long3 _e101 = input_uniform.val_i64_3_;
+    metal::long3 _e104 = input_storage.val_i64_3_;
+    output.val_i64_3_ = as_type<metal::long3>(as_type<metal::ulong3>(_e101) + as_type<metal::ulong3>(_e104));
+    metal::long4 _e110 = input_uniform.val_i64_4_;
+    metal::long4 _e113 = input_storage.val_i64_4_;
+    output.val_i64_4_ = as_type<metal::long4>(as_type<metal::ulong4>(_e110) + as_type<metal::ulong4>(_e113));
+    type_12 _e119 = input_arrays.val_i64_array_2_;
+    output_arrays.val_i64_array_2_ = _e119;
+    long _e120 = val;
     long _e122 = val;
+    val = as_type<long>(as_type<ulong>(_e122) + as_type<ulong>(naga_abs(_e120)));
     long _e124 = val;
-    val = as_type<long>(as_type<ulong>(_e124) + as_type<ulong>(naga_abs(_e122)));
+    long _e125 = val;
     long _e126 = val;
-    long _e127 = val;
     long _e128 = val;
+    val = as_type<long>(as_type<ulong>(_e128) + as_type<ulong>(metal::clamp(_e124, _e125, _e126)));
     long _e130 = val;
-    val = as_type<long>(as_type<ulong>(_e130) + as_type<ulong>(metal::clamp(_e126, _e127, _e128)));
+    metal::long2 _e131 = metal::long2(_e130);
     long _e132 = val;
     metal::long2 _e133 = metal::long2(_e132);
-    long _e134 = val;
-    metal::long2 _e135 = metal::long2(_e134);
+    long _e135 = val;
+    val = as_type<long>(as_type<ulong>(_e135) + as_type<ulong>(( + _e131.x * _e133.x + _e131.y * _e133.y)));
     long _e137 = val;
-    val = as_type<long>(as_type<ulong>(_e137) + as_type<ulong>(( + _e133.x * _e135.x + _e133.y * _e135.y)));
-    long _e139 = val;
+    long _e138 = val;
     long _e140 = val;
+    val = as_type<long>(as_type<ulong>(_e140) + as_type<ulong>(metal::max(_e137, _e138)));
     long _e142 = val;
-    val = as_type<long>(as_type<ulong>(_e142) + as_type<ulong>(metal::max(_e139, _e140)));
-    long _e144 = val;
+    long _e143 = val;
     long _e145 = val;
+    val = as_type<long>(as_type<ulong>(_e145) + as_type<ulong>(metal::min(_e142, _e143)));
     long _e147 = val;
-    val = as_type<long>(as_type<ulong>(_e147) + as_type<ulong>(metal::min(_e144, _e145)));
     long _e149 = val;
+    val = as_type<long>(as_type<ulong>(_e149) + as_type<ulong>(metal::select(metal::select(long(-1), long(1), (_e147 > 0)), long(0), (_e147 == 0))));
     long _e151 = val;
-    val = as_type<long>(as_type<ulong>(_e151) + as_type<ulong>(metal::select(metal::select(long(-1), long(1), (_e149 > 0)), long(0), (_e149 == 0))));
-    long _e153 = val;
-    return _e153;
+    return _e151;
 }
 
 ulong uint64_function(