ANSI C requires that a call to an unprototyped function type succeed

if the definition has a non-variadic prototype with compatible
parameters.  Therefore, the default rule for such calls must be to
use a non-variadic convention.  Achieve this by casting the callee to
the function type with which it is required to be compatible, unless
the target specifically opts out and insists that unprototyped calls
should use the variadic rules.  The only case of that I'm aware of is
the x86-64 convention, which passes arguments the same way in both
cases but also sets a small amount of extra information;  here we seek
to maintain compatibility with GCC, which does set this when calling
an unprototyped function.

Addresses PR10810 and PR10713.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@140241 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 17 insertions, 0 deletions

diff --git a/lib/CodeGen/TargetInfo.cpp b/lib/CodeGen/TargetInfo.cpp
index 434e202f2e..bad8a1d928 100644
--- a/lib/CodeGen/TargetInfo.cpp
+++ b/lib/CodeGen/TargetInfo.cpp
@@ -98,6 +98,14 @@ unsigned TargetCodeGenInfo::getSizeOfUnwindException() const {
   return 32;
 }
 
+bool TargetCodeGenInfo::isNoProtoCallVariadic(CallingConv CC) const {
+  // The following conventions are known to require this to be false:
+  //   x86_stdcall
+  //   MIPS
+  // For everything else, we just prefer false unless we opt out.
+  return false;
+}
+
 static bool isEmptyRecord(ASTContext &Context, QualType T, bool AllowArrays);
 
 /// isEmptyField - Return true iff a the field is "empty", that is it
@@ -959,6 +967,15 @@ public:
     return X86AdjustInlineAsmType(CGF, Constraint, Ty);
   }
 
+  bool isNoProtoCallVariadic(CallingConv CC) const {
+    // The default CC on x86-64 sets %al to the number of SSA
+    // registers used, and GCC sets this when calling an unprototyped
+    // function, so we override the default behavior.
+    if (CC == CC_Default || CC == CC_C) return true;
+
+    return TargetCodeGenInfo::isNoProtoCallVariadic(CC);
+  }
+
 };
 
 class WinX86_64TargetCodeGenInfo : public TargetCodeGenInfo {