diff options
| -rw-r--r-- | lib/Target/X86/README.txt | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt index 79f8e64..9618d9c 100644 --- a/lib/Target/X86/README.txt +++ b/lib/Target/X86/README.txt @@ -662,3 +662,29 @@ call _foo Obviously it would have been better for the first mov (or any op) to store directly %esp[0] if there are no other uses. + +//===---------------------------------------------------------------------===// + +Is it really a good idea to use movlhps to move 1 double-precision FP value from +low quadword of source to high quadword of destination? + +e.g. + +void test2 (v2sd *b, double X, double Y) { + v2sd a = (v2sd) {X, X*Y}; + *b = a; +} + + movsd 8(%esp), %xmm0 + movapd %xmm0, %xmm1 + mulsd 16(%esp), %xmm1 + movlhps %xmm1, %xmm0 + movl 4(%esp), %eax + movapd %xmm0, (%eax) + ret + +icc uses unpcklpd instead. + +//===---------------------------------------------------------------------===// + +Use movhps and movlhps to update upper 64-bits of a v4sf value. |