http://llvm.org/bugs/show_bug.cgi?id=17725
Bug ID: 17725
Summary: use the right data type when materializing an FP
constant
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
In the following code example, llvm is using the single-precision "xorps" to
materialize an FP double 0.0 constant.
Intel warns that there may be a performance penalty for mixing data types
("execution domains" in Intel-speak; see related bug 17185).
It would be better to use "xorpd" here to avoid that penalty:
$ cat addfp0.c
double foo(double x) {
return 0.0 + x;
}
$ ./clang -O3 -fomit-frame-pointer -o - -S addfp0.c
.section __TEXT,__text,regular,pure_instructions
.globl _foo
.align 4, 0x90
_foo: ## @foo
.cfi_startproc
## BB#0: ## %entry
xorps %xmm1, %xmm1 <---- use "xorpd" here
addsd %xmm0, %xmm1
movaps %xmm1, %xmm0
ret
.cfi_endproc
.subsections_via_symbols
$ ./clang -v
clang version 3.4 (trunk 193529) (llvm/trunk 193527)
Target: x86_64-apple-darwin11.4.2
Thread model: posix
--
You are receiving this mail because:
You are on the CC list for the bug.
_______________________________________________
LLVMbugs mailing list
[email protected]
http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs
