mir-opt tests fail on big endian

[nikic]

A number of mir-opt tests fail on s390x, which is a big endian architecture. Failures for 1.79:

---- [mir-opt] tests/mir-opt/const_debuginfo.rs stdout ----
106	  }
107	  
108	  ALLOC0 (size: 8, align: 4) {
-	      20 00 00 00 20 00 00 00                         │  ... ...
+	      00 00 00 20 00 00 00 20                         │ ... ... 
110	  }
111	  
112	  ALLOC1 (size: 4, align: 2) {
-	      01 00 63 00                                     │ ..c.
+	      00 01 00 63                                     │ ...c
114	  }
115	  
116	
thread '[mir-opt] tests/mir-opt/const_debuginfo.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/const_debuginfo.main.ConstDebugInfo.diff
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
---- [mir-opt] tests/mir-opt/const_prop/address_of_pair.rs stdout ----
47	+ }
48	+ 
49	+ ALLOC0 (size: 8, align: 4) {
-	+     01 00 00 00 00 __ __ __                         │ .....░░░
+	+     00 00 00 01 00 __ __ __                         │ .....░░░
51	  }
52	  
53	
thread '[mir-opt] tests/mir-opt/const_prop/address_of_pair.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/const_prop/address_of_pair.fn0.GVN.diff
---- [mir-opt] tests/mir-opt/const_prop/checked_add.rs stdout ----
27	+ }
28	+ 
29	+ ALLOC0 (size: 8, align: 4) {
-	+     02 00 00 00 00 __ __ __                         │ .....░░░
+	+     00 00 00 02 00 __ __ __                         │ .....░░░
31	  }
32	  
33	
thread '[mir-opt] tests/mir-opt/const_prop/checked_add.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/const_prop/checked_add.main.GVN.panic-unwind.diff
---- [mir-opt] tests/mir-opt/const_prop/mutable_variable_aggregate.rs stdout ----
27	+ }
28	+ 
29	+ ALLOC0 (size: 8, align: 4) {
-	+     2a 00 00 00 2b 00 00 00                         │ *...+...
+	+     00 00 00 2a 00 00 00 2b                         │ ...*...+
31	  }
32	  
33	
thread '[mir-opt] tests/mir-opt/const_prop/mutable_variable_aggregate.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/const_prop/mutable_variable_aggregate.main.GVN.diff
---- [mir-opt] tests/mir-opt/const_prop/mutable_variable_aggregate_mut_ref.rs stdout ----
34	+ }
35	+ 
36	+ ALLOC0 (size: 8, align: 4) {
-	+     2a 00 00 00 2b 00 00 00                         │ *...+...
+	+     00 00 00 2a 00 00 00 2b                         │ ...*...+
38	  }
39	  
40	
thread '[mir-opt] tests/mir-opt/const_prop/mutable_variable_aggregate_mut_ref.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/const_prop/mutable_variable_aggregate_mut_ref.main.GVN.diff
---- [mir-opt] tests/mir-opt/const_prop/mutable_variable_unprop_assign.rs stdout ----
51	+ }
52	+ 
53	+ ALLOC0 (size: 8, align: 4) {
-	+     01 00 00 00 02 00 00 00                         │ ........
+	+     00 00 00 01 00 00 00 02                         │ ........
55	  }
56	  
57	
thread '[mir-opt] tests/mir-opt/const_prop/mutable_variable_unprop_assign.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/const_prop/mutable_variable_unprop_assign.main.GVN.panic-unwind.diff
---- [mir-opt] tests/mir-opt/const_prop/return_place.rs stdout ----
20	+ }
21	+ 
22	+ ALLOC0 (size: 8, align: 4) {
-	+     04 00 00 00 00 __ __ __                         │ .....░░░
+	+     00 00 00 04 00 __ __ __                         │ .....░░░
24	  }
25	  
26	
thread '[mir-opt] tests/mir-opt/const_prop/return_place.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/const_prop/return_place.add.GVN.panic-unwind.diff
---- [mir-opt] tests/mir-opt/const_prop/slice_len.rs stdout ----
52	+ }
53	+ 
54	+ ALLOC0 (size: 12, align: 4) {
-	+     01 00 00 00 02 00 00 00 03 00 00 00             │ ............
+	+     00 00 00 01 00 00 00 02 00 00 00 03             │ ............
56	  }
57	  
58	
thread '[mir-opt] tests/mir-opt/const_prop/slice_len.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/const_prop/slice_len.main.GVN.64bit.panic-unwind.diff
---- [mir-opt] tests/mir-opt/const_prop/tuple_literal_propagation.rs stdout ----
34	+ }
35	+ 
36	+ ALLOC0 (size: 8, align: 4) {
-	+     01 00 00 00 02 00 00 00                         │ ........
+	+     00 00 00 01 00 00 00 02                         │ ........
38	  }
39	  
40	
thread '[mir-opt] tests/mir-opt/const_prop/tuple_literal_propagation.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/const_prop/tuple_literal_propagation.main.GVN.panic-unwind.diff
---- [mir-opt] tests/mir-opt/dataflow-const-prop/default_boxed_slice.rs stdout ----
109	+ }
110	+ 
111	+ ALLOC2 (size: 16, align: 8) {
-	+     01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
+	+     00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 00 │ ................
113	+ }
114	+ 
115	+ ALLOC1 (size: 16, align: 8) {
-	+     01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
+	+     00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 00 │ ................
117	+ }
118	+ 
119	+ ALLOC0 (size: 16, align: 8) {
-	+     01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
+	+     00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 00 │ ................
121	  }
122	  
123	
thread '[mir-opt] tests/mir-opt/dataflow-const-prop/default_boxed_slice.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.GVN.64bit.panic-unwind.diff
---- [mir-opt] tests/mir-opt/dataflow-const-prop/checked.rs stdout ----
79	+ }
80	+ 
81	+ ALLOC0 (size: 8, align: 4) {
-	+     00 00 00 80 01 __ __ __                         │ .....░░░
+	+     80 00 00 00 01 __ __ __                         │ .....░░░
83	+ }
84	+ 
85	+ ALLOC1 (size: 8, align: 4) {
-	+     03 00 00 00 00 __ __ __                         │ .....░░░
+	+     00 00 00 03 00 __ __ __                         │ .....░░░
87	  }
88	  
89	
thread '[mir-opt] tests/mir-opt/dataflow-const-prop/checked.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/dataflow-const-prop/checked.main.DataflowConstProp.panic-unwind.diff
---- [mir-opt] tests/mir-opt/dataflow-const-prop/enum.rs stdout ----
122	  }
123	  
124	  ALLOC0 (size: 8, align: 4) {
-	      01 00 00 00 04 00 00 00                         │ ........
+	      00 00 00 01 00 00 00 04                         │ ........
126	  }
127	  
128	  ALLOC1 (static: statics::C, size: 8, align: 4) {
thread '[mir-opt] tests/mir-opt/dataflow-const-prop/enum.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/dataflow-const-prop/enum.statics.DataflowConstProp.64bit.diff
---- [mir-opt] tests/mir-opt/dataflow-const-prop/struct.rs stdout ----
200	+ }
201	+ 
202	+ ALLOC6 (size: 8, align: 4) {
-	+     01 00 00 00 23 00 00 00                         │ ....#...
+	+     00 00 00 01 00 00 00 23                         │ .......#
204	+ }
205	+ 
206	+ ALLOC7 (size: 8, align: 4) {
-	+     01 00 00 00 23 00 00 00                         │ ....#...
+	+     00 00 00 01 00 00 00 23                         │ .......#
208	+ }
209	+ 
210	+ ALLOC8 (size: 8, align: 4) {
-	+     01 00 00 00 23 00 00 00                         │ ....#...
+	+     00 00 00 01 00 00 00 23                         │ .......#
212	+ }
213	+ 
214	+ ALLOC9 (size: 8, align: 4) {
-	+     01 00 00 00 01 00 00 00                         │ ........
+	+     00 00 00 01 00 00 00 01                         │ ........
216	+ }
217	+ 
218	+ ALLOC10 (size: 4, align: 4) {
-	+     01 00 00 00                                     │ ....
+	+     00 00 00 01                                     │ ....
220	  }
221	  
222	  ALLOC5 (static: BIG_STAT, size: 8, align: 8) {
224	  }
225	  
226	  ALLOC0 (size: 32, align: 8) {
-	      0x00 │ 01 00 00 00 23 00 00 00 ╾ALLOC1<imm>╼ │ ....#...╾──────╼
-	      0x10 │ 02 00 00 00 00 00 00 00 00 00 a4 42 __ __ __ __ │ ...........B░░░░
+	      0x00 │ 00 00 00 01 00 00 00 23 ╾ALLOC1<imm>╼ │ .......#╾──────╼
+	      0x10 │ 00 00 00 00 00 00 00 02 42 a4 00 00 __ __ __ __ │ ........B...░░░░
229	  }
230	  
231	  ALLOC1 (size: 8, align: 4) {
-	      00 00 34 42 00 00 90 42                         │ ..4B...B
+	      42 34 00 00 42 90 00 00                         │ B4..B...
233	  }
234	  
235	  ALLOC4 (static: SMALL_STAT, size: 8, align: 8) {
238	  
239	  ALLOC2 (size: 32, align: 8) {
240	      0x00 │ 00 00 00 00 __ __ __ __ ╾ALLOC3<imm>╼ │ ....░░░░╾──────╼
-	      0x10 │ 01 00 00 00 00 00 00 00 00 00 10 41 __ __ __ __ │ ...........A░░░░
+	      0x10 │ 00 00 00 00 00 00 00 01 41 10 00 00 __ __ __ __ │ ........A...░░░░
242	  }
243	  
244	  ALLOC3 (size: 4, align: 4) {
-	      00 00 50 41                                     │ ..PA
+	      41 50 00 00                                     │ AP..
246	  }
247	  
248	
thread '[mir-opt] tests/mir-opt/dataflow-const-prop/struct.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/dataflow-const-prop/struct.main.DataflowConstProp.64bit.diff
---- [mir-opt] tests/mir-opt/dataflow-const-prop/tuple.rs stdout ----
95	+ }
96	+ 
97	+ ALLOC0 (size: 8, align: 4) {
-	+     02 00 00 00 03 00 00 00                         │ ........
+	+     00 00 00 02 00 00 00 03                         │ ........
99	+ }
100	+ 
101	+ ALLOC1 (size: 8, align: 4) {
-	+     02 00 00 00 03 00 00 00                         │ ........
+	+     00 00 00 02 00 00 00 03                         │ ........
103	+ }
104	+ 
105	+ ALLOC2 (size: 8, align: 4) {
-	+     02 00 00 00 03 00 00 00                         │ ........
+	+     00 00 00 02 00 00 00 03                         │ ........
107	+ }
108	+ 
109	+ ALLOC3 (size: 8, align: 4) {
-	+     01 00 00 00 02 00 00 00                         │ ........
+	+     00 00 00 01 00 00 00 02                         │ ........
111	  }
112	  
113	
thread '[mir-opt] tests/mir-opt/dataflow-const-prop/tuple.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/dataflow-const-prop/tuple.main.DataflowConstProp.64bit.diff
---- [mir-opt] tests/mir-opt/enum_opt.rs stdout ----
67	+ }
68	+ 
69	+ ALLOC0 (size: 16, align: 8) {
-	+     05 20 00 00 00 00 00 00 01 00 00 00 00 00 00 00 │ . ..............
+	+     00 00 00 00 00 00 20 05 00 00 00 00 00 00 00 01 │ ...... .........
71	  }
72	  
73	
thread '[mir-opt] tests/mir-opt/enum_opt.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/enum_opt.unin.EnumSizeOpt.64bit.diff
---- [mir-opt] tests/mir-opt/gvn.rs stdout ----
179	+ }
180	+ 
181	+ ALLOC1 (size: 16, align: 8) {
-	+     01 00 00 00 00 00 00 00 02 00 00 00 00 00 00 00 │ ................
+	+     00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 02 │ ................
183	+ }
184	+ 
185	+ ALLOC0 (size: 16, align: 8) {
-	+     01 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 │ ................
+	+     00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 01 │ ................
187	  }
188	  
189	
thread '[mir-opt] tests/mir-opt/gvn.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/gvn.wide_ptr_integer.GVN.panic-unwind.diff
---- [mir-opt] tests/mir-opt/pre-codegen/optimizes_into_variable.rs stdout ----
64	+ }
65	+ 
66	+ ALLOC0 (size: 8, align: 4) {
-	+     04 00 00 00 00 __ __ __                         │ .....░░░
+	+     00 00 00 04 00 __ __ __                         │ .....░░░
68	  }
69	  
70	
thread '[mir-opt] tests/mir-opt/pre-codegen/optimizes_into_variable.rs' panicked at src/tools/compiletest/src/runtest.rs:4421:21:
Actual MIR output differs from expected MIR output /builddir/build/BUILD/rust-1.79.0~beta.10-build/rustc-beta-src/tests/mir-opt/pre-codegen/optimizes_into_variable.main.GVN.64bit.panic-unwind.diff
failures:
    [mir-opt] tests/mir-opt/const_debuginfo.rs
    [mir-opt] tests/mir-opt/const_prop/address_of_pair.rs
    [mir-opt] tests/mir-opt/const_prop/checked_add.rs
    [mir-opt] tests/mir-opt/const_prop/mutable_variable_aggregate.rs
    [mir-opt] tests/mir-opt/const_prop/mutable_variable_aggregate_mut_ref.rs
    [mir-opt] tests/mir-opt/const_prop/mutable_variable_unprop_assign.rs
    [mir-opt] tests/mir-opt/const_prop/return_place.rs
    [mir-opt] tests/mir-opt/const_prop/slice_len.rs
    [mir-opt] tests/mir-opt/const_prop/tuple_literal_propagation.rs
    [mir-opt] tests/mir-opt/dataflow-const-prop/default_boxed_slice.rs
    [mir-opt] tests/mir-opt/dataflow-const-prop/checked.rs
    [mir-opt] tests/mir-opt/dataflow-const-prop/enum.rs
    [mir-opt] tests/mir-opt/dataflow-const-prop/struct.rs
    [mir-opt] tests/mir-opt/dataflow-const-prop/tuple.rs
    [mir-opt] tests/mir-opt/enum_opt.rs
    [mir-opt] tests/mir-opt/gvn.rs
    [mir-opt] tests/mir-opt/pre-codegen/optimizes_into_variable.rs

Some previous fixes for such failures were #115167 and #106046.

[nikic]

Something peculiar about many of these tests is that transforms seem to create ALLOCs that are not actually referenced by MIR. Is that expected?

In terms of fixing this, the existing approach of picking constants that are endianness-independent doesn't seem very scalable. Maybe it would make sense to have a flag that disables dumping the contents of allocations? I think that for most of these tests they are not relevant (especially as the allocations are unused in the first place).

[DianQK]

Something peculiar about many of these tests is that transforms seem to create ALLOCs that are not actually referenced by MIR. Is that expected?

This appears to be an intermediate result of the optimization process, such as: https://rust.godbolt.org/z/ohz1YMqez (tests/mir-opt/const_prop/slice_len.rs).

In terms of fixing this, the existing approach of picking constants that are endianness-independent doesn't seem very scalable. Maybe it would make sense to have a flag that disables dumping the contents of allocations? I think that for most of these tests they are not relevant (especially as the allocations are unused in the first place).

There is an option ignore-endian-big to skip these tests, but I like another option to change the output to be uniformly little-endian.

[cuviper]

If these tests don't actually care about the raw bytes in their UI comparisons, then they can use normalize-stderr-test to hide the bytes. There are quite a few tests that already normalize to the string "HEX_DUMP".

[cuviper]

Rather than trying to normalize output, I'm proposing an option in #126502 to skip the raw bytes altogether.