When generating code for X86 targets, make sure the fp control word is set
to 64-bit precision, not 80 bits.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@18915 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/CBackend/CBackend.cpp b/lib/Target/CBackend/CBackend.cpp
index dc8ce2e..c922586 100644
--- a/lib/Target/CBackend/CBackend.cpp
+++ b/lib/Target/CBackend/CBackend.cpp
@@ -214,6 +214,7 @@
unsigned Indent);
void printIndexingExpression(Value *Ptr, gep_type_iterator I,
gep_type_iterator E);
+ void printCodeForMain();
};
}
@@ -1127,6 +1128,9 @@
Out << "\n";
+ if (F.hasExternalLinkage() && F.getName() == "main")
+ printCodeForMain();
+
// print the basic blocks
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
if (Loop *L = LI->getLoopFor(BB)) {
@@ -1140,6 +1144,15 @@
Out << "}\n\n";
}
+void CWriter::printCodeForMain() {
+ // On X86, set the FP control word to 64-bits of precision instead of 80 bits.
+ Out << "#if defined(__GNUC__) && !defined(__llvm__)\n"
+ << "#if defined(i386) || defined(__i386__) || defined(__i386)\n"
+ << "{short FPCW;__asm__ (\"fnstcw %0\" : \"=m\" (*&FPCW));\n"
+ << "FPCW=(FPCW&~0x300)|0x200;__asm__(\"fldcw %0\" :: \"m\" (*&FPCW));}\n"
+ << "#endif\n#endif\n";
+}
+
void CWriter::printLoop(Loop *L) {
Out << " do { /* Syntactic loop '" << L->getHeader()->getName()
<< "' to make GCC happy */\n";