R600: Add work-around for the CF stack entry HW bug

The CF stack can be corrupted if you use CF_ALU_PUSH_BEFORE,
CF_ALU_ELSE_AFTER, CF_ALU_BREAK, or CF_ALU_CONTINUE when the number of
sub-entries on the stack is greater than or equal to the stack entry
size and sub-entries modulo 4 is either 0 or 3 (on cedar the bug is
present when number of sub-entries module 8 is either 7 or 0)

We choose to be conservative and always apply the work-around when the
number of sub-enries is greater than or equal to the stack entry size,
so that we can safely over-allocate the stack when we are unsure of the
stack allocation rules.

reviewed-by: Vincent Lejeune <vljn at ovi.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199842 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/R600/AMDGPUSubtarget.cpp

@@ -39,6 +39,7 @@ AMDGPUSubtarget::AMDGPUSubtarget(StringRef TT, StringRef CPU, StringRef FS) :
   EnableIRStructurizer = true;
   EnableIfCvt = true;
   WavefrontSize = 0;
+  CFALUBug = false;
   ParseSubtargetFeatures(GPU, FS);
   DevName = GPU;
 }
@@ -97,6 +98,11 @@ AMDGPUSubtarget::getStackEntrySize() const {
   }
 }
 bool
+AMDGPUSubtarget::hasCFAluBug() const {
+  assert(getGeneration() <= NORTHERN_ISLANDS);
+  return CFALUBug;
+}
+bool
 AMDGPUSubtarget::isTargetELF() const {
   return false;
 }