When the "true" and "false" blocks of a diamond if-conversion are the same,

do not double-count the duplicate instructions by counting once from the
beginning and again from the end.  Keep track of where the duplicates from
the beginning ended and don't go past that point when counting duplicates
at the end.  Radar 8589805.

This change causes one of the MC/ARM/simple-fp-encoding tests to produce
different (better!) code without the vmovne instruction being tested.
I changed the test to produce vmovne and vmoveq instructions but moving
between register files in the opposite direction.  That's not quite the same
but predicated versions of those instructions weren't being tested before,
so at least the test coverage is not any worse, just different.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117333 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 46 insertions, 52 deletions

diff --git a/lib/CodeGen/IfConversion.cpp b/lib/CodeGen/IfConversion.cpp
index ce3eda7891..e90985bf89 100644
--- a/lib/CodeGen/IfConversion.cpp
+++ b/lib/CodeGen/IfConversion.cpp
@@ -520,18 +520,6 @@ bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
   return TExit && TExit == FalseBBI.BB;
 }
 
-static
-MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
-                                               const TargetInstrInfo *TII) {
-  MachineBasicBlock::iterator I = BB->end();
-  while (I != BB->begin()) {
-    --I;
-    if (!I->getDesc().isBranch())
-      break;
-  }
-  return I;
-}
-
 /// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
 /// with their common predecessor) forms a valid diamond shape for ifcvt.
 bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
@@ -560,64 +548,70 @@ bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
       (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
     return false;
 
-  MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
-  MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
+  // Count duplicate instructions at the beginning of the true and false blocks.
+  MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
+  MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
   MachineBasicBlock::iterator TIE = TrueBBI.BB->end();
   MachineBasicBlock::iterator FIE = FalseBBI.BB->end();
-  // Skip dbg_value instructions
-  while (TI != TIE && TI->isDebugValue())
-    ++TI;
-  while (FI != FIE && FI->isDebugValue())
-    ++FI;
-  while (TI != TIE && FI != FIE) {
+  while (TIB != TIE && FIB != FIE) {
     // Skip dbg_value instructions. These do not count.
-    if (TI->isDebugValue()) {
-      while (TI != TIE && TI->isDebugValue())
-        ++TI;
-      if (TI == TIE)
+    if (TIB->isDebugValue()) {
+      while (TIB != TIE && TIB->isDebugValue())
+        ++TIB;
+      if (TIB == TIE)
         break;
     }
-    if (FI->isDebugValue()) {
-      while (FI != FIE && FI->isDebugValue())
-        ++FI;
-      if (FI == FIE)
+    if (FIB->isDebugValue()) {
+      while (FIB != FIE && FIB->isDebugValue())
+        ++FIB;
+      if (FIB == FIE)
         break;
     }
-    if (!TI->isIdenticalTo(FI))
+    if (!TIB->isIdenticalTo(FIB))
       break;
     ++Dups1;
-    ++TI;
-    ++FI;
+    ++TIB;
+    ++FIB;
   }
 
-  TI = firstNonBranchInst(TrueBBI.BB, TII);
-  FI = firstNonBranchInst(FalseBBI.BB, TII);
-  MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
-  MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
-  // Skip dbg_value instructions at end of the bb's.
-  while (TI != TIB && TI->isDebugValue())
-    --TI;
-  while (FI != FIB && FI->isDebugValue())
-    --FI;
-  while (TI != TIB && FI != FIB) {
+  // Now, in preparation for counting duplicate instructions at the ends of the
+  // blocks, move the end iterators up past any branch instructions.
+  while (TIE != TIB) {
+    --TIE;
+    if (!TIE->getDesc().isBranch())
+      break;
+  }
+  while (FIE != FIB) {
+    --FIE;
+    if (!FIE->getDesc().isBranch())
+      break;
+  }
+
+  // If Dups1 includes all of a block, then don't count duplicate
+  // instructions at the end of the blocks.
+  if (TIB == TIE || FIB == FIE)
+    return true;
+
+  // Count duplicate instructions at the ends of the blocks.
+  while (TIE != TIB && FIE != FIB) {
     // Skip dbg_value instructions. These do not count.
-    if (TI->isDebugValue()) {
-      while (TI != TIB && TI->isDebugValue())
-        --TI;
-      if (TI == TIB)
+    if (TIE->isDebugValue()) {
+      while (TIE != TIB && TIE->isDebugValue())
+        --TIE;
+      if (TIE == TIB)
         break;
     }
-    if (FI->isDebugValue()) {
-      while (FI != FIB && FI->isDebugValue())
-        --FI;
-      if (FI == FIB)
+    if (FIE->isDebugValue()) {
+      while (FIE != FIB && FIE->isDebugValue())
+        --FIE;
+      if (FIE == FIB)
         break;
     }
-    if (!TI->isIdenticalTo(FI))
+    if (!TIE->isIdenticalTo(FIE))
       break;
     ++Dups2;
-    --TI;
-    --FI;
+    --TIE;
+    --FIE;
   }
 
   return true;