[PATCH] D92907: [RegisterClassInfo] Return non-zero for RC without allocatable reg

[Jinsong Ji via Phabricator via llvm-commits]

jsji updated this revision to Diff 314613.
jsji added a comment.

Update comments.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D92907/new/

https://reviews.llvm.org/D92907

Files:
  llvm/lib/CodeGen/RegisterClassInfo.cpp
  llvm/test/CodeGen/PowerPC/compute-regpressure.ll


Index: llvm/test/CodeGen/PowerPC/compute-regpressure.ll
===================================================================
--- llvm/test/CodeGen/PowerPC/compute-regpressure.ll
+++ llvm/test/CodeGen/PowerPC/compute-regpressure.ll
@@ -1,7 +1,7 @@
 ; REQUIRES: asserts
 ; RUN: llc -debug-only=regalloc < %s 2>&1 |FileCheck %s --check-prefix=DEBUG
 
-; DEBUG-COUNT-3:         AllocationOrder(VRSAVERC) = [ ]
+; DEBUG-COUNT-1:         AllocationOrder(VRSAVERC) = [ ]
 
 target triple = "powerpc64le-unknown-linux-gnu"
 
Index: llvm/lib/CodeGen/RegisterClassInfo.cpp
===================================================================
--- llvm/lib/CodeGen/RegisterClassInfo.cpp
+++ llvm/lib/CodeGen/RegisterClassInfo.cpp
@@ -188,7 +188,14 @@
   }
   assert(RC && "Failed to find register class");
   compute(RC);
-  unsigned NReserved = RC->getNumRegs() - getNumAllocatableRegs(RC);
-  return TRI->getRegPressureSetLimit(*MF, Idx) -
-         TRI->getRegClassWeight(RC).RegWeight * NReserved;
+  unsigned NAllocatableRegs = getNumAllocatableRegs(RC);
+  unsigned RegPressureSetLimit = TRI->getRegPressureSetLimit(*MF, Idx);
+  // If all the regs are reserved, return raw RegPressureSetLimit.
+  // One example is VRSAVERC in PowerPC.
+  // Avoid returning zero, getRegPressureSetLimit(Idx) assumes computePSetLimit
+  // return non-zero value.
+  if (NAllocatableRegs == 0)
+    return RegPressureSetLimit;
+  unsigned NReserved = RC->getNumRegs() - NAllocatableRegs;
+  return RegPressureSetLimit - TRI->getRegClassWeight(RC).RegWeight * NReserved;
 }


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