silly assembly for comparing the result of comparisons that return Int# against 0#

Consider the module

{-# LANGUAGE MagicHash #-}
module Min where

import GHC.Exts

fgood :: Int# -> Int# -> Int
fgood x# y# = case isTrue# (x# <# y#) of
  False -> I# y#
  True  -> I# x#

fbad :: Int# -> Int# -> Int
fbad x# y# = case x# <# y# of
  0# -> I# y#
  _  -> I# x#

The code for fgood looks fine:

0000000000000130 <Min_fgood_info>:
 130:	49 83 c4 10          	add    $0x10,%r12
 134:	4d 3b a5 58 03 00 00 	cmp    0x358(%r13),%r12
 13b:	77 1a                	ja     157 <Min_fgood_info+0x27>
 13d:	49 39 f6             	cmp    %rsi,%r14
 140:	7c 29                	jl     16b <Min_fgood_info+0x3b>
 142:	49 c7 44 24 f8 00 00 	movq   $0x0,-0x8(%r12)
 149:	00 00 
			147: R_X86_64_32S	ghczmprim_GHCziTypes_Izh_con_info
 14b:	49 89 34 24          	mov    %rsi,(%r12)
 14f:	49 8d 5c 24 f9       	lea    -0x7(%r12),%rbx
 154:	ff 65 00             	jmpq   *0x0(%rbp)
 157:	49 c7 85 88 03 00 00 	movq   $0x10,0x388(%r13)
 15e:	10 00 00 00 
 162:	bb 00 00 00 00       	mov    $0x0,%ebx
			163: R_X86_64_32	Min_fgood_closure
 167:	41 ff 65 f8          	jmpq   *-0x8(%r13)
 16b:	49 c7 44 24 f8 00 00 	movq   $0x0,-0x8(%r12)
 172:	00 00 
			170: R_X86_64_32S	ghczmprim_GHCziTypes_Izh_con_info
 174:	4d 89 34 24          	mov    %r14,(%r12)
 178:	49 8d 5c 24 f9       	lea    -0x7(%r12),%rbx
 17d:	ff 65 00             	jmpq   *0x0(%rbp)

But the code for fbad has several problems:

0000000000000018 <Min_fbad_info>:
  18:	48 8d 45 f0          	lea    -0x10(%rbp),%rax
  1c:	4c 39 f8             	cmp    %r15,%rax
  1f:	72 3a                	jb     5b <Min_fbad_info+0x43>
  21:	48 89 f0             	mov    %rsi,%rax
  24:	4c 89 f3             	mov    %r14,%rbx
  27:	49 39 f6             	cmp    %rsi,%r14
  2a:	0f 9c c1             	setl   %cl
  2d:	0f b6 c9             	movzbl %cl,%ecx
  30:	48 85 c9             	test   %rcx,%rcx
  33:	75 51                	jne    86 <c1Sm_info+0xe>
  35:	49 83 c4 10          	add    $0x10,%r12
  39:	4d 3b a5 58 03 00 00 	cmp    0x358(%r13),%r12
  40:	0f 87 aa 00 00 00    	ja     f0 <c1Su_info+0x10>
  46:	49 c7 44 24 f8 00 00 	movq   $0x0,-0x8(%r12)
  4d:	00 00 
			4b: R_X86_64_32S	ghczmprim_GHCziTypes_Izh_con_info
  4f:	49 89 04 24          	mov    %rax,(%r12)
  53:	49 8d 5c 24 f9       	lea    -0x7(%r12),%rbx
  58:	ff 65 00             	jmpq   *0x0(%rbp)
  5b:	bb 00 00 00 00       	mov    $0x0,%ebx
			5c: R_X86_64_32	Min_fbad_closure
  60:	41 ff 65 f8          	jmpq   *-0x8(%r13)
	...

; c1Sm_info is the other case with its own heap check and GC entry code
; c1Su_info is another GC entry
; in total, another 160 bytes of code

For some reason, the heap checks were moved into the alternatives, which was not a good decision in this case. But the silly thing here is the cmp/setl/movzbl/test/jne sequence in Min_fbad_info, which should be replaced by a cmp/jl as in Min_fgood_info.

Same behavior in 7.8 and HEAD.

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (CodeGen)
Test case
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