[RegAllocGreedy][Last Chance Recoloring] Emit diagnostics when last chance

recoloring cut-offs are hit.

This is related to PR18747.

Patch by MAYUR PANDEY <mayur.p@samsung.com>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205599 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 35 insertions, 1 deletions

diff --git a/lib/CodeGen/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp
index 6a623b8200..923ec3e800 100644
--- a/lib/CodeGen/RegAllocGreedy.cpp
+++ b/lib/CodeGen/RegAllocGreedy.cpp
@@ -37,6 +37,7 @@
 #include "llvm/CodeGen/RegAllocRegistry.h"
 #include "llvm/CodeGen/RegisterClassInfo.h"
 #include "llvm/CodeGen/VirtRegMap.h"
+#include "llvm/IR/LLVMContext.h"
 #include "llvm/PassAnalysisSupport.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
@@ -147,6 +148,22 @@ class RAGreedy : public MachineFunctionPass,
     RS_Done
   };
 
+  // Enum CutOffStage to keep a track whether the register allocation failed
+  // because of the cutoffs encountered in last chance recoloring.
+  // Note: This is used as bitmask. New value should be next power of 2.
+  enum CutOffStage {
+    // No cutoffs encountered
+    CO_None = 0,
+
+    // lcr-max-depth cutoff encountered
+    CO_Depth = 1,
+
+    // lcr-max-interf cutoff encountered
+    CO_Interf = 2
+  };
+
+  uint8_t CutOffInfo;
+
 #ifndef NDEBUG
   static const char *const StageName[];
 #endif
@@ -1912,6 +1929,7 @@ RAGreedy::mayRecolorAllInterferences(unsigned PhysReg, LiveInterval &VirtReg,
     if (Q.collectInterferingVRegs(LastChanceRecoloringMaxInterference) >=
         LastChanceRecoloringMaxInterference) {
       DEBUG(dbgs() << "Early abort: too many interferences.\n");
+      CutOffInfo |= CO_Interf;
       return false;
     }
     for (unsigned i = Q.interferingVRegs().size(); i; --i) {
@@ -1984,6 +2002,7 @@ unsigned RAGreedy::tryLastChanceRecoloring(LiveInterval &VirtReg,
   // Indeed, in that case we may want to cut the search space earlier.
   if (Depth >= LastChanceRecoloringMaxDepth) {
     DEBUG(dbgs() << "Abort because max depth has been reached.\n");
+    CutOffInfo |= CO_Depth;
     return ~0u;
   }
 
@@ -2108,8 +2127,23 @@ bool RAGreedy::tryRecoloringCandidates(PQueue &RecoloringQueue,
 
 unsigned RAGreedy::selectOrSplit(LiveInterval &VirtReg,
                                  SmallVectorImpl<unsigned> &NewVRegs) {
+  CutOffInfo = CO_None;
+  LLVMContext &Ctx = MF->getFunction()->getContext();
   SmallVirtRegSet FixedRegisters;
-  return selectOrSplitImpl(VirtReg, NewVRegs, FixedRegisters);
+  unsigned Reg = selectOrSplitImpl(VirtReg, NewVRegs, FixedRegisters);
+  if (Reg == ~0U && (CutOffInfo != CO_None)) {
+    uint8_t CutOffEncountered = CutOffInfo & (CO_Depth | CO_Interf);
+    if (CutOffEncountered == CO_Depth)
+      Ctx.emitError(
+          "register allocation failed: maximum depth for recoloring reached");
+    else if (CutOffEncountered == CO_Interf)
+      Ctx.emitError("register allocation failed: maximum interference for "
+                    "recoloring reached");
+    else if (CutOffEncountered == (CO_Depth | CO_Interf))
+      Ctx.emitError("register allocation failed: maximum interference and "
+                    "depth for recoloring reached");
+  }
+  return Reg;
 }
 
 /// Using a CSR for the first time has a cost because it causes push|pop