diff options
Diffstat (limited to 'lib/Target/X86/README-X86-64.txt')
| -rw-r--r-- | lib/Target/X86/README-X86-64.txt | 44 |
1 files changed, 0 insertions, 44 deletions
diff --git a/lib/Target/X86/README-X86-64.txt b/lib/Target/X86/README-X86-64.txt index 78c4dc0..e21d69a 100644 --- a/lib/Target/X86/README-X86-64.txt +++ b/lib/Target/X86/README-X86-64.txt @@ -41,50 +41,6 @@ saved a few instructions. //===---------------------------------------------------------------------===// -Poor codegen: - -int X[2]; -int b; -void test(void) { - memset(X, b, 2*sizeof(X[0])); -} - -llc: - movq _b@GOTPCREL(%rip), %rax - movzbq (%rax), %rax - movq %rax, %rcx - shlq $8, %rcx - orq %rax, %rcx - movq %rcx, %rax - shlq $16, %rax - orq %rcx, %rax - movq %rax, %rcx - shlq $32, %rcx - movq _X@GOTPCREL(%rip), %rdx - orq %rax, %rcx - movq %rcx, (%rdx) - ret - -gcc: - movq _b@GOTPCREL(%rip), %rax - movabsq $72340172838076673, %rdx - movzbq (%rax), %rax - imulq %rdx, %rax - movq _X@GOTPCREL(%rip), %rdx - movq %rax, (%rdx) - ret - -And the codegen is even worse for the following -(from http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33103): - void fill1(char *s, int a) - { - __builtin_memset(s, a, 15); - } - -For this version, we duplicate the computation of the constant to store. - -//===---------------------------------------------------------------------===// - It's not possible to reference AH, BH, CH, and DH registers in an instruction requiring REX prefix. However, divb and mulb both produce results in AH. If isel emits a CopyFromReg which gets turned into a movb and that can be allocated a |