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Remove some README.txt entries which are now implemented.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92511 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-01-04 20:55:05 +00:00
parent 44c92e5826
commit 3c02c22ef9
1 changed files with 3 additions and 80 deletions
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83
lib/Target/X86/README.txt
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@ -530,7 +530,7 @@ We should inline lrintf and probably other libc functions.
//===---------------------------------------------------------------------===//
Start using the flags more. For example, compile:
Use the FLAGS values from arithmetic instructions more. For example, compile:
int add_zf(int *x, int y, int a, int b) {
if ((*x += y) == 0)
@ -554,31 +554,8 @@ _add_zf:
movl %ecx, %eax
ret
and:
int add_zf(int *x, int y, int a, int b) {
if ((*x + y) < 0)
return a;
else
return b;
}
to:
add_zf:
addl (%rdi), %esi
movl %edx, %eax
cmovns %ecx, %eax
ret
instead of:
_add_zf:
addl (%rdi), %esi
testl %esi, %esi
cmovs %edx, %ecx
movl %ecx, %eax
ret
As another example, compile function f2 in test/CodeGen/X86/cmp-test.ll
without a test instruction.
//===---------------------------------------------------------------------===//
@ -685,55 +662,6 @@ Though this probably isn't worth it.
//===---------------------------------------------------------------------===//
We need to teach the codegen to convert two-address INC instructions to LEA
when the flags are dead (likewise dec). For example, on X86-64, compile:
int foo(int A, int B) {
return A+1;
}
to:
_foo:
leal 1(%edi), %eax
ret
instead of:
_foo:
incl %edi
movl %edi, %eax
ret
Another example is:
;; X's live range extends beyond the shift, so the register allocator
;; cannot coalesce it with Y. Because of this, a copy needs to be
;; emitted before the shift to save the register value before it is
;; clobbered. However, this copy is not needed if the register
;; allocator turns the shift into an LEA. This also occurs for ADD.
; Check that the shift gets turned into an LEA.
; RUN: llvm-as < %s | llc -march=x86 -x86-asm-syntax=intel | \
; RUN: not grep {mov E.X, E.X}
@G = external global i32 ; <i32*> [#uses=3]
define i32 @test1(i32 %X, i32 %Y) {
%Z = add i32 %X, %Y ; <i32> [#uses=1]
volatile store i32 %Y, i32* @G
volatile store i32 %Z, i32* @G
ret i32 %X
}
define i32 @test2(i32 %X) {
%Z = add i32 %X, 1 ; <i32> [#uses=1]
volatile store i32 %Z, i32* @G
ret i32 %X
}
//===---------------------------------------------------------------------===//
Sometimes it is better to codegen subtractions from a constant (e.g. 7-x) with
a neg instead of a sub instruction. Consider:
@ -852,11 +780,6 @@ __Z11no_overflowjj:
ret
//===---------------------------------------------------------------------===//
Re-materialize MOV32r0 etc. with xor instead of changing them to moves if the
condition register is dead. xor reg reg is shorter than mov reg, #0.
//===---------------------------------------------------------------------===//
The following code: