[PATCH] D37899: [SystemZ] Implement shouldCoalesce() to help regalloc to avoid running out of registers with GR128 regs

[Jonas Paulsson via Phabricator via llvm-commits]

jonpa created this revision.

Fix for https://bugs.llvm.org/show_bug.cgi?id=34610

Regalloc runs out of registers in a test case with GR128 register. This can be remedied by not allowing coalescing copys of subregs from GR128 regs in shouldCoalesce().


https://reviews.llvm.org/D37899

Files:
  lib/Target/SystemZ/SystemZRegisterInfo.cpp
  lib/Target/SystemZ/SystemZRegisterInfo.h
  test/CodeGen/SystemZ/regalloc-GR128.ll


Index: test/CodeGen/SystemZ/regalloc-GR128.ll
===================================================================
--- /dev/null
+++ test/CodeGen/SystemZ/regalloc-GR128.ll
@@ -0,0 +1,11 @@
+; RUN: llc < %s -mtriple=s390x-linux-gnu -mcpu=z13 -O3 |& FileCheck %s
+;
+; Test that regalloc does not run out of registers
+
+define i64 @test(i64 %dividend, i64 %divisor) {
+; CHECK-NOT: LLVM ERROR: ran out of registers during register allocation
+init:
+  %rem = urem i64 %dividend, %divisor
+  call void asm sideeffect "", "{r1},{r3},{r5},{r7},{r9},{r11},{r12},{r13}"(i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 %rem)
+  ret i64 %rem
+}
Index: lib/Target/SystemZ/SystemZRegisterInfo.h
===================================================================
--- lib/Target/SystemZ/SystemZRegisterInfo.h
+++ lib/Target/SystemZ/SystemZRegisterInfo.h
@@ -59,6 +59,14 @@
   void eliminateFrameIndex(MachineBasicBlock::iterator MI,
                            int SPAdj, unsigned FIOperandNum,
                            RegScavenger *RS) const override;
+ bool shouldCoalesce(MachineInstr *MI,
+                      const TargetRegisterClass *SrcRC,
+                      unsigned SubReg,
+                      const TargetRegisterClass *DstRC,
+                      unsigned DstSubReg,
+                      const TargetRegisterClass *NewRC) const override;
+
+  /// \brief SrcRC and DstRC will be morphed into NewRC if this returns true.
   unsigned getFrameRegister(const MachineFunction &MF) const override;
 };
 
Index: lib/Target/SystemZ/SystemZRegisterInfo.cpp
===================================================================
--- lib/Target/SystemZ/SystemZRegisterInfo.cpp
+++ lib/Target/SystemZ/SystemZRegisterInfo.cpp
@@ -152,6 +152,22 @@
   MI->getOperand(FIOperandNum + 1).ChangeToImmediate(Offset);
 }
 
+bool SystemZRegisterInfo::shouldCoalesce(MachineInstr *MI,
+                                  const TargetRegisterClass *SrcRC,
+                                  unsigned SubReg,
+                                  const TargetRegisterClass *DstRC,
+                                  unsigned DstSubReg,
+                                  const TargetRegisterClass *NewRC) const {
+  // Avoid coalescing COPYs of subregs of a GR128 register to prevent
+  // regalloc running out of registers. That may happen as long as subreg
+  // liveness is turned off per default due to being compile time expensive.
+  if (SrcRC->hasSubClassEq(&SystemZ::GR128BitRegClass) &&
+      getRegSizeInBits(*DstRC) <= 64)
+    return false;
+
+  return true;
+}
+
 unsigned
 SystemZRegisterInfo::getFrameRegister(const MachineFunction &MF) const {
   const SystemZFrameLowering *TFI = getFrameLowering(MF);


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