https://llvm.org/bugs/show_bug.cgi?id=23522
Bug ID: 23522
Summary: Optimized assembly raises div-by-zero exception though
C source code takes pains to avoid it
Product: clang
Version: unspecified
Hardware: Macintosh
OS: MacOS X
Status: NEW
Severity: normal
Priority: P
Component: -New Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Created attachment 14326
--> https://llvm.org/bugs/attachment.cgi?id=14326&action=edit
Program showing clang optimization bug
The attached C program takes care to avoid division by zero when presented with
a = b = 0.0. It works correctly when compiled without optimization (using -O0).
When compiler optimization level -O1 or above is used, the assembly generated:
movsd -16(%rbp), %xmm0
mulsd %xmm0, %xmm0
movsd -24(%rbp), %xmm1
mulsd %xmm1, %xmm1
addsd %xmm0, %xmm1
movsd LCPI0_0(%rip), %xmm0
divsd %xmm1, %xmm0
cmpltsd LCPI0_1(%rip), %xmm1
movapd %xmm1, %xmm2
andnpd %xmm0, %xmm2
movsd LCPI0_2(%rip), %xmm0
andpd %xmm1, %xmm0
orpd %xmm2, %xmm0
sqrtsd %xmm0, %xmm0
performs a floating-point division before checking for zero denominator and
hence raises a div-by-zero exception:
clang -O1 optbug.c
./a.out
Input a, b: 0 0
Floating exception
--
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
