[PATCH] AAPCS: Cannot split argument between GPRs and the stack after a CPRC has been allocated to the stack

[Oliver Stannard]

================
Comment at: lib/CodeGen/TargetInfo.cpp:3481
@@ -3457,1 +3480,3 @@
+    // the stack.
+    AllocatedVFP = 17;
     return;
----------------
Renato Golin wrote:
> Oliver Stannard wrote:
> > Renato Golin wrote:
> > > Why are you saturating? Is there any place that especially check against 17? Or are all of them like this, >=16?
> > On line 3336, we check whether AllocatedVFP > 16, as we need to know whether some CPRCs have been allocated on the stack.
> Shouldn't we just change that check, then? I think it makes more sense.
This can't be done just by changing the check.

Without the line "AllocatedVFP = 17;", AllocatedVFPs will be set to 16 for the following two cases:
 * 8 doubles - exactly fills the VFP registers
 * 9 doubles - fills the VFP registers with no gaps, plus one double on the stack

However, we need to differentiate between the two cases, as in the first we can split a struct between the GPRs and stack, but in the second case we cannot. (AAPCS rule C.5)

Because of this, I am using (AllocatedVFPs > NumVFPs) to signify that at least one CPRC has been allocated to the stack, and the same with AllocatedGPRs. Once AllocatedVFPs > NumVFPs, we don't actually need to track the exact number of bytes used on the stack, only that this is non-zero.


http://llvm-reviews.chandlerc.com/D2726