[Peephole] Allow folding loads into instructions w/multiple uses (such as test64rr)

Peephole opt has a one use limitation which appears to be accidental. The function being used was incorrectly documented as returning whether the def had one *user*, but instead returned true only when there was one *use*. Add a corresponding hasOneNonDbgUser helper, and adjust peephole-opt to use the appropriate one.

All of the actual folding code handles multiple uses within a single instruction. That codepath is well exercised through instruction selection.

Differential Revision: https://reviews.llvm.org/D63656

llvm-svn: 364336

2 files changed, 10 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/MachineRegisterInfo.cpp b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
index be4b13bcef2..f0fd0405d69 100644
--- a/llvm/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
@@ -423,6 +423,13 @@ bool MachineRegisterInfo::hasOneNonDBGUse(unsigned RegNo) const {
   return ++UI == use_nodbg_end();
 }
 
+bool MachineRegisterInfo::hasOneNonDBGUser(unsigned RegNo) const {
+  use_instr_nodbg_iterator UI = use_instr_nodbg_begin(RegNo);
+  if (UI == use_instr_nodbg_end())
+    return false;
+  return ++UI == use_instr_nodbg_end();
+}
+
 /// clearKillFlags - Iterate over all the uses of the given register and
 /// clear the kill flag from the MachineOperand. This function is used by
 /// optimization passes which extend register lifetimes and need only
diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index a3f1b83b157..38512e5a1a7 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -1306,7 +1306,7 @@ bool PeepholeOptimizer::optimizeUncoalescableCopy(
 
 /// Check whether MI is a candidate for folding into a later instruction.
 /// We only fold loads to virtual registers and the virtual register defined
-/// has a single use.
+/// has a single user.
 bool PeepholeOptimizer::isLoadFoldable(
     MachineInstr &MI, SmallSet<unsigned, 16> &FoldAsLoadDefCandidates) {
   if (!MI.canFoldAsLoad() || !MI.mayLoad())
@@ -1316,12 +1316,12 @@ bool PeepholeOptimizer::isLoadFoldable(
     return false;
 
   unsigned Reg = MI.getOperand(0).getReg();
-  // To reduce compilation time, we check MRI->hasOneNonDBGUse when inserting
+  // To reduce compilation time, we check MRI->hasOneNonDBGUser when inserting
   // loads. It should be checked when processing uses of the load, since
   // uses can be removed during peephole.
   if (!MI.getOperand(0).getSubReg() &&
       TargetRegisterInfo::isVirtualRegister(Reg) &&
-      MRI->hasOneNonDBGUse(Reg)) {
+      MRI->hasOneNonDBGUser(Reg)) {
     FoldAsLoadDefCandidates.insert(Reg);
     return true;
   }