[CodeGenPrepare] Fix counting uses when folding addresses into memory instructions

The counter of the number of instructions seen in `FindAllMemoryUses`
is reset after returning from a recursive invocation of
`FindAllMemoryUses` to the value it had before the call. In effect,
depending on the shape of the uses graph, the function may scan up to
`2^N-1` instructions where `N` is the scan limit
(`MaxMemoryUsesToScan`).  This does not look intuitive or intended.

This patch changes the counting to just count the scanned
instructions, independent of the shape of the references.

Reviewed By: mkazantsev

Differential Revision: https://reviews.llvm.org/D143893

Change-Id: I99f5de55e84843cf2fbea287d6ae4312fa196240

1 files changed, 13 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index ddbba80..db3aa72 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -4972,7 +4972,7 @@ static bool FindAllMemoryUses(
     Instruction *I, SmallVectorImpl<std::pair<Value *, Type *>> &MemoryUses,
     SmallPtrSetImpl<Instruction *> &ConsideredInsts, const TargetLowering &TLI,
     const TargetRegisterInfo &TRI, bool OptSize, ProfileSummaryInfo *PSI,
-    BlockFrequencyInfo *BFI, int SeenInsts = 0) {
+    BlockFrequencyInfo *BFI, int &SeenInsts) {
   // If we already considered this instruction, we're done.
   if (!ConsideredInsts.insert(I).second)
     return false;
@@ -5043,6 +5043,17 @@ static bool FindAllMemoryUses(
   return false;
 }
 
+static bool FindAllMemoryUses(
+    Instruction *I, SmallVectorImpl<std::pair<Value *, Type *>> &MemoryUses,
+    const TargetLowering &TLI, const TargetRegisterInfo &TRI, bool OptSize,
+    ProfileSummaryInfo *PSI, BlockFrequencyInfo *BFI) {
+  int SeenInsts = 0;
+  SmallPtrSet<Instruction *, 16> ConsideredInsts;
+  return FindAllMemoryUses(I, MemoryUses, ConsideredInsts, TLI, TRI, OptSize,
+                           PSI, BFI, SeenInsts);
+}
+
+
 /// Return true if Val is already known to be live at the use site that we're
 /// folding it into. If so, there is no cost to include it in the addressing
 /// mode. KnownLive1 and KnownLive2 are two values that we know are live at the
@@ -5125,9 +5136,7 @@ bool AddressingModeMatcher::isProfitableToFoldIntoAddressingMode(
   // for another (at worst.)  In this context, folding an addressing mode into
   // the use is just a particularly nice way of sinking it.
   SmallVector<std::pair<Value *, Type *>, 16> MemoryUses;
-  SmallPtrSet<Instruction *, 16> ConsideredInsts;
-  if (FindAllMemoryUses(I, MemoryUses, ConsideredInsts, TLI, TRI, OptSize, PSI,
-                        BFI))
+  if (FindAllMemoryUses(I, MemoryUses, TLI, TRI, OptSize, PSI, BFI))
     return false; // Has a non-memory, non-foldable use!
 
   // Now that we know that all uses of this instruction are part of a chain of