Rollup merge of #106046 - uweigand:s390x-test-bigendian-mir, r=Mark-Simulacrum

Fix mir-opt tests for big-endian platforms

The test cases src/test/mir-opt/building/custom/consts.rs and src/test/mir-opt/const_prop/mutable_variable_no_prop.rs are currently failing on big-endian platforms as the binary encoding of some constants is hard-coded in the MIR test files.  Fix this by choosing constant values that have the same encoding on big- and little-endian platforms.

The test case src/test/mir-opt/issues/issue_75439.rs is failing as well, but since the purpose of the test is to validate handling of big-endian integer encodings on a little-endian platform, it does not make much sense to run it on big-endian platforms in the first place - we can just ignore it there.

Fixed part of https://github.com/rust-lang/rust/issues/105383.

tests/mir-opt/building/custom/consts.rs

@@ -18,8 +18,8 @@ fn consts<const C: u32>() {
     })
 }
 
-static S: i32 = 5;
+static S: i32 = 0x05050505;
-static mut T: i32 = 10;
+static mut T: i32 = 0x0a0a0a0a;
 // EMIT_MIR consts.statics.built.after.mir
 #[custom_mir(dialect = "built")]
 fn statics() {

tests/mir-opt/building/custom/consts.statics.built.after.mir

@@ -19,9 +19,9 @@ fn statics() -> () {
 }
 
 alloc2 (static: T, size: 4, align: 4) {
-    0a 00 00 00                                     │ ....
+    0a 0a 0a 0a                                     │ ....
 }
 
 alloc1 (static: S, size: 4, align: 4) {
-    05 00 00 00                                     │ ....
+    05 05 05 05                                     │ ....
 }

tests/mir-opt/const_prop/mutable_variable_no_prop.main.ConstProp.diff

@@ -38,6 +38,6 @@
   }
   
   alloc1 (static: STATIC, size: 4, align: 4) {
-      2a 00 00 00                                     │ *...
+      42 42 42 42                                     │ BBBB
   }
   

tests/mir-opt/const_prop/mutable_variable_no_prop.rs

@@ -1,7 +1,7 @@
 // unit-test
 // compile-flags: -O
 
-static mut STATIC: u32 = 42;
+static mut STATIC: u32 = 0x42424242;
 
 // EMIT_MIR mutable_variable_no_prop.main.ConstProp.diff
 fn main() {

tests/mir-opt/issues/issue_75439.foo.MatchBranchSimplification.diff

@@ -26,7 +26,7 @@
           _3 = _1;                         // scope 2 at $DIR/issue_75439.rs:+2:47: +2:52
           _2 = transmute::<[u8; 16], [u32; 4]>(move _3) -> bb1; // scope 2 at $DIR/issue_75439.rs:+2:37: +2:53
                                            // mir::Constant
-                                           // + span: $DIR/issue_75439.rs:7:37: 7:46
+                                           // + span: $DIR/issue_75439.rs:8:37: 8:46
                                            // + literal: Const { ty: unsafe extern "rust-intrinsic" fn([u8; 16]) -> [u32; 4] {transmute::<[u8; 16], [u32; 4]>}, val: Value(<ZST>) }
       }
   
@@ -49,7 +49,7 @@
           _6 = _4;                         // scope 4 at $DIR/issue_75439.rs:+5:33: +5:35
           _5 = transmute::<u32, [u8; 4]>(move _6) -> bb7; // scope 4 at $DIR/issue_75439.rs:+5:23: +5:36
                                            // mir::Constant
-                                           // + span: $DIR/issue_75439.rs:10:23: 10:32
+                                           // + span: $DIR/issue_75439.rs:11:23: 11:32
                                            // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(u32) -> [u8; 4] {transmute::<u32, [u8; 4]>}, val: Value(<ZST>) }
       }
   

tests/mir-opt/issues/issue_75439.rs

@@ -1,4 +1,5 @@
 // EMIT_MIR issue_75439.foo.MatchBranchSimplification.diff
+// ignore-endian-big
 
 use std::mem::transmute;