Subzero: Deterministically sort constant pool entries.

tests_lit/llvm2ice_tests/elf_container.ll

 ; Tests that we generate an ELF container with fields that make sense,
 ; cross-validating against llvm-mc.
 
 ; For the integrated ELF writer, we can't pipe the output because we need
 ; to seek backward and patch up the file headers. So, use a temporary file.
 ; RUN: %p2i -i %s --filetype=obj --args -O2 --verbose none -o %t \
 ; RUN:   && llvm-readobj -file-headers -sections -section-data \
 ; RUN:       -relocations -symbols %t | FileCheck %s
 
 ; RUN: %if --need=allow_dump --command %p2i -i %s --args -O2 --verbose none \
@@ skipping 293 matching lines @@
 ; CHECK:       SHF_MERGE
 ; CHECK:     ]
 ; CHECK:     Address: 0x0
 ; CHECK:     Offset: 0x{{[1-9A-F][0-9A-F]*}}
 ; CHECK:     Size: 8
 ; CHECK:     Link: 0
 ; CHECK:     Info: 0
 ; CHECK:     AddressAlignment: 4
 ; CHECK:     EntrySize: 4
 ; CHECK:     SectionData (
-; CHECK:       0000: A0709D3F 00000080
+; CHECK:       0000: 00000080 A0709D3F
 ; CHECK:     )
 ; CHECK:   }
 ; CHECK:   Section {
 ; CHECK:     Index: {{[1-9][0-9]*}}
 ; CHECK:     Name: .rodata.cst8
 ; CHECK:     Type: SHT_PROGBITS
 ; CHECK:     Flags [ (0x12)
 ; CHECK:       SHF_ALLOC
 ; CHECK:       SHF_MERGE
 ; CHECK:     ]
@@ skipping 88 matching lines @@
 ; CHECK-NEXT:     Name: (0)
 ; CHECK-NEXT:     Value: 0x0
 ; CHECK-NEXT:     Size: 0
 ; CHECK-NEXT:     Binding: Local
 ; CHECK-NEXT:     Type: None
 ; CHECK-NEXT:     Other: 0
 ; CHECK-NEXT:     Section: Undefined (0x0)
 ; CHECK-NEXT:   }
 ; CHECK:        Symbol {
 ; CHECK:          Name: .L$double$0
 ; CHECK-NEXT:     Value: 0x10

[jvoung (off chromium), 2015/04/08 15:03:28]

a bit surprised that L$double$0 and $1 didn't switch places

[Jim Stichnoth, 2015/04/08 22:34:30]

(Note: For whatever reason (oversight?), .L$double$0 and .L$double$2 are
checked, but not .L$double$1.)

If you look as the -filetype=asm output (after this patch), you get:

	.section	.rodata.cst4,"aM",@progbits,4
	.align	4
.L$float$0:
	.long	0x80000000	# float -0.000000e+00
.L$float$1:
	.long	0x3f9d70a0	# float 1.230000e+00
	.section	.rodata.cst8,"aM",@progbits,8
	.align	8
.L$double$2:
	.quad	0xfff8000000000003	# double -nan
.L$double$1:
	.quad	0xfff7ffffffffffff	# double -nan
.L$double$0:
	.quad	0xffffffffffffffff	# double -nan

The values within each section are indeed sorted by bit representation, if you
squint hard enough and realize that the comparison function is memcmp() on the
little-endian representation.  Then I'm guessing that llvm-readobj is sorting
its dump output by Name.

However, this made me realize that this memcmp() based comparison function will
lead to different results when Subzero is run on a big-endian machine (if that's
even a thing these days).  So I changed it to use a bitcast style operation and
then compare using an integer type.

This once again changes the output order, such that the .long and .quad values
appear properly sorted.  Note that this gets obscured a bit in the llvm-readobj
output since these values are output little-endian.

 ; CHECK-NEXT:     Size: 0
 ; CHECK-NEXT:     Binding: Local (0x0)
 ; CHECK-NEXT:     Type: None (0x0)
 ; CHECK-NEXT:     Other: 0
 ; CHECK-NEXT:     Section: .rodata.cst8
 ; CHECK-NEXT:   }
 ; CHECK:        Symbol {
 ; CHECK:          Name: .L$double$2
 ; CHECK-NEXT:     Value: 0x0
 ; CHECK-NEXT:     Size: 0
 ; CHECK-NEXT:     Binding: Local (0x0)
 ; CHECK-NEXT:     Type: None (0x0)
 ; CHECK-NEXT:     Other: 0
 ; CHECK-NEXT:     Section: .rodata.cst8
 ; CHECK-NEXT:   }
 ; CHECK:        Symbol {
 ; CHECK:          Name: .L$float$0
-; CHECK-NEXT:     Value: 0x4
+; CHECK-NEXT:     Value: 0x0
 ; CHECK-NEXT:     Size: 0
 ; CHECK-NEXT:     Binding: Local (0x0)
 ; CHECK-NEXT:     Type: None (0x0)
 ; CHECK-NEXT:     Other: 0
 ; CHECK-NEXT:     Section: .rodata.cst4
 ; CHECK-NEXT:   }
 ; CHECK:        Symbol {
 ; CHECK:          Name: .L$float$1
-; CHECK-NEXT:     Value: 0x0
+; CHECK-NEXT:     Value: 0x4
 ; CHECK-NEXT:     Size: 0
 ; CHECK-NEXT:     Binding: Local (0x0)
 ; CHECK-NEXT:     Type: None (0x0)
 ; CHECK-NEXT:     Other: 0
 ; CHECK-NEXT:     Section: .rodata.cst4
 ; CHECK-NEXT:   }
 ; CHECK:        Symbol {
 ; CHECK:          Name: addend_ptr
 ; CHECK-NEXT:     Value: 0x18
 ; CHECK-NEXT:     Size: 4
@@ skipping 177 matching lines @@
 ; CHECK:        Symbol {
 ; CHECK:          Name: memset
 ; CHECK-NEXT:     Value: 0x0
 ; CHECK-NEXT:     Size: 0
 ; CHECK-NEXT:     Binding: Global
 ; CHECK-NEXT:     Type: None
 ; CHECK-NEXT:     Other: 0
 ; CHECK-NEXT:     Section: Undefined
 ; CHECK-NEXT:   }
 ; CHECK: ]