The hash function for MI expressions, used by MachineCSE, is really

broken. This patch fixes the superficial problems which lead to the
intractably slow compile times reported in PR13225.

The specific issue is that we were failing to include the *offset* of
a global variable in the hash code. Oops. This would in turn cause all
MIs which were only distinguishable due to operating on different
offsets of a global variable to produce identical hash functions. In
some of the test cases attached to the PR I saw hash table activity
where there were O(1000) probes-per-lookup *on average*. A very few
entries were responsible for most of these probes.

There is still quite a bit more to do here. The ad-hoc layering of data
in MachineOperands makes them *extremely* brittle to hash correctly.
We're missing quite a few other cases, the only ones I've fixed here are
the specific MO types which were allowed through the assert() in
getOffset().

llvm-svn: 159741

1 files changed, 8 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index 85b5e398646..0ee0213d9a4 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -1882,19 +1882,24 @@ MachineInstrExpressionTrait::getHashValue(const MachineInstr* const &MI) {
       HashComponents.push_back(hash_combine(MO.getType(), MO.getImm()));
       break;
     case MachineOperand::MO_FrameIndex:
-    case MachineOperand::MO_ConstantPoolIndex:
     case MachineOperand::MO_JumpTableIndex:
       HashComponents.push_back(hash_combine(MO.getType(), MO.getIndex()));
       break;
+    case MachineOperand::MO_ConstantPoolIndex:
+      HashComponents.push_back(hash_combine(MO.getType(), MO.getIndex(),
+                                            MO.getOffset()));
+      break;
     case MachineOperand::MO_MachineBasicBlock:
       HashComponents.push_back(hash_combine(MO.getType(), MO.getMBB()));
       break;
     case MachineOperand::MO_GlobalAddress:
-      HashComponents.push_back(hash_combine(MO.getType(), MO.getGlobal()));
+      HashComponents.push_back(hash_combine(MO.getType(), MO.getGlobal(),
+                                            MO.getOffset()));
       break;
     case MachineOperand::MO_BlockAddress:
       HashComponents.push_back(hash_combine(MO.getType(),
-                                            MO.getBlockAddress()));
+                                            MO.getBlockAddress(),
+                                            MO.getOffset()));
       break;
     case MachineOperand::MO_MCSymbol:
       HashComponents.push_back(hash_combine(MO.getType(), MO.getMCSymbol()));