[LLVMbugs] [Bug 21173] New: stack protector generating sse3 instructions in unoptimized 32-bit build

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21173

            Bug ID: 21173
           Summary: stack protector generating sse3 instructions in
                    unoptimized 32-bit build
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: phantall+llvm at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

clang --version
echo 'void test() { char blah[127] = {}; }' | clang++ -g -m32 -xc++ -c -o
/tmp/blah1.o
echo 'void test() { char blah[127] = {}; }' | clang++ -g -fstack-protector-all
-Wstack-protector -m32 -xc++ -c -o /tmp/blah2.o


If you look at the disassembly for /tmp/blah{1,2}.o, the former generates some
instructions that are valid for any of the Pentium processors, whereas the
latter uses %xmm0 & movaps instructions to initialize `blah`.

Without really digging into it I can only speculate, but my best guess is stack
protector is potentially enabling one or more optimizations that would
otherwise not be enabled in a typical debug build w/out optimizations.

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