http://llvm.org/bugs/show_bug.cgi?id=2520
Summary: fabs not marked readnone
Product: tools
Version: trunk
Platform: PC
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P2
Component: llvm-gcc
AssignedTo: [EMAIL PROTECTED]
ReportedBy: [EMAIL PROTECTED]
CC: [email protected]
According to fabs(3), none of fabs fabsf or fabsl can have any errors. As such,
they should be marked readnone since all they ever do is return their own
input.
$ cat fabs.c
#include <math.h>
double f(double *x, double *y) { return fabs(*x + *y); }
$ llvm-gcc -O2 fabs.c -S -o - -emit-llvm
; ModuleID = 'fabs.c'
target datalayout =
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"
target triple = "i386-pc-linux-gnu"
define double @f(double* %x, double* %y) nounwind {
entry:
%tmp2 = load double* %x, align 8 ; <double> [#uses=1]
%tmp4 = load double* %y, align 8 ; <double> [#uses=1]
%tmp5 = add double %tmp2, %tmp4 ; <double> [#uses=1]
%tmp6 = tail call double @fabs( double %tmp5 ) ; <double>
[#uses=1]
ret double %tmp6
}
declare double @fabs(double)
This stops some optimizations from working (GVN in particular) because it
doesn't know that fabs() won't be writing to one of the double* arguments.
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