diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Target/X86/README.txt | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt index 41b38d8..567d5c4 100644 --- a/lib/Target/X86/README.txt +++ b/lib/Target/X86/README.txt @@ -1429,3 +1429,65 @@ Possible optimizations: + } + } //===---------------------------------------------------------------------===// + +main () +{ + int i = 0; + unsigned long int z = 0; + + do { + z -= 0x00004000; + i++; + if (i > 0x00040000) + abort (); + } while (z > 0); + exit (0); +} + +gcc compiles this to: + +_main: + subl $28, %esp + xorl %eax, %eax + jmp L2 +L3: + cmpl $262144, %eax + je L10 +L2: + addl $1, %eax + cmpl $262145, %eax + jne L3 + call L_abort$stub +L10: + movl $0, (%esp) + call L_exit$stub + +llvm: + +_main: + subl $12, %esp + movl $1, %eax + movl $16384, %ecx +LBB1_1: # bb + cmpl $262145, %eax + jge LBB1_4 # cond_true +LBB1_2: # cond_next + incl %eax + addl $4294950912, %ecx + cmpl $16384, %ecx + jne LBB1_1 # bb +LBB1_3: # bb11 + xorl %eax, %eax + addl $12, %esp + ret +LBB1_4: # cond_true + call L_abort$stub + +1. LSR should rewrite the first cmp with induction variable %ecx. +2. DAG combiner should fold + leal 1(%eax), %edx + cmpl $262145, %edx + => + cmpl $262144, %eax + +//===---------------------------------------------------------------------===// |