[Pipeliner] Check for affine expression in isLoopCarriedOrder

The pipeliner must add a loop carried dependence between two memory
operations if the base register is not an affine (linear) exression.
The current implementation doesn't check how the base register is
defined, which allows non-affine expressions, and then the pipeliner
does not add a loop carried dependence when one is needed.

This patch adds code to isLoopCarriedOrder that checks if the base
register of the memory operations is defined by a phi, and the loop
definition for the phi is a constant increment value.  This is a very
simple check for a linear expression.

Patch by Brendon Cahoon.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328550 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 13 insertions, 1 deletions

diff --git a/lib/CodeGen/MachinePipeliner.cpp b/lib/CodeGen/MachinePipeliner.cpp
index 8015eda1605..c7c5a4a91d0 100644
--- a/lib/CodeGen/MachinePipeliner.cpp
+++ b/lib/CodeGen/MachinePipeliner.cpp
@@ -2647,7 +2647,6 @@ void SwingSchedulerDAG::generateExistingPhis(
     unsigned NumPhis = std::min(NumStages, MaxPhis);
 
     unsigned NewReg = 0;
-
     unsigned AccessStage = (LoopValStage != -1) ? LoopValStage : StageScheduled;
     // In the epilog, we may need to look back one stage to get the correct
     // Phi name because the epilog and prolog blocks execute the same stage.
@@ -3562,6 +3561,19 @@ bool SwingSchedulerDAG::isLoopCarriedDep(SUnit *Source, const SDep &Dep,
   if (BaseRegS != BaseRegD)
     return true;
 
+  // Check that the base register is incremented by a constant value for each
+  // iteration.
+  MachineInstr *Def = MRI.getVRegDef(BaseRegS);
+  if (!Def || !Def->isPHI())
+    return true;
+  unsigned InitVal = 0;
+  unsigned LoopVal = 0;
+  getPhiRegs(*Def, BB, InitVal, LoopVal);
+  MachineInstr *LoopDef = MRI.getVRegDef(LoopVal);
+  int D = 0;
+  if (!LoopDef || !TII->getIncrementValue(*LoopDef, D))
+    return true;
+
   uint64_t AccessSizeS = (*SI->memoperands_begin())->getSize();
   uint64_t AccessSizeD = (*DI->memoperands_begin())->getSize();