[PATCH] Handle resolvable branches in complete loop unroll heuristic.

[Michael Zolotukhin]

Hi chandlerc,

Resolving a branch allows us to ignore blocks that won't be executed, and thus make our estimate more accurate.
This patch is intended to be applied after D10205 (though it could be applied independently).

http://reviews.llvm.org/D10206

Files:
  lib/Transforms/Scalar/LoopUnrollPass.cpp

Index: lib/Transforms/Scalar/LoopUnrollPass.cpp
===================================================================
--- lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -418,6 +418,28 @@
 
     return true;
   }
+
+  bool visitCmpInst(CmpInst &I) {
+    if (SCEVSimplify(&I))
+      return true;
+    Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
+    // First try to handle simplified comparisons.
+    if (!isa<Constant>(LHS))
+      if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS))
+        LHS = SimpleLHS;
+    if (!isa<Constant>(RHS))
+      if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS))
+        RHS = SimpleRHS;
+    if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
+      if (Constant *CRHS = dyn_cast<Constant>(RHS))
+        if (Constant *C = ConstantExpr::getCompare(I.getPredicate(), CLHS, CRHS)) {
+          SimplifiedValues[&I] = C;
+          return true;
+        }
+    }
+
+    return false;
+  }
 };
 } // namespace
 
@@ -496,6 +518,28 @@
           return None;
       }
 
+      TerminatorInst *TI = BB->getTerminator();
+
+      // Add in the live successors by first checking whether we have terminator
+      // that may be simplified based on the values simplified by this call.
+      if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+        if (BI->isConditional()) {
+          Value *Cond = BI->getCondition();
+          if (ConstantInt *SimpleCond
+              = dyn_cast_or_null<ConstantInt>(SimplifiedValues.lookup(Cond))) {
+            BBWorklist.insert(BI->getSuccessor(SimpleCond->isZero() ? 1 : 0));
+            continue;
+          }
+        }
+      } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+        Value *Cond = SI->getCondition();
+        if (ConstantInt *SimpleCond
+            = dyn_cast_or_null<ConstantInt>(SimplifiedValues.lookup(Cond))) {
+          BBWorklist.insert(SI->findCaseValue(SimpleCond).getCaseSuccessor());
+          continue;
+        }
+      }
+
       // Add BB's successors to the worklist.
       for (BasicBlock *Succ : successors(BB))
         if (L->contains(Succ))

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D10206.27021.patch
Type: text/x-patch
Size: 2125 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20150603/8b57ff02/attachment.bin>