commit a958cbfe367ed7bf6a3a260b28a7b19cf70b7d9f
author Chris Lattner <sabre@nondot.org> Mon Jan 11 22:45:25 2010 +0000
committer Chris Lattner <sabre@nondot.org> Mon Jan 11 22:45:25 2010 +0000
tree cd1c296c59282e94bdfa21a20cee1162a77e1d22
parent 92f238dd8fe19b26103bd451c571281d9b7ad324

Disable folding sext(trunc(x)) -> x (and other similar cast/cast cases) when the 
trunc has multiple uses.  Codegen is not able to coalesce the subreg case 
correctly and so this leads to higher register pressure and spilling (see PR5997).

This speeds up 256.bzip2 from 8.60 -> 8.04s on my machine, ~7%.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93200 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstCombineCasts.cpp

diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 939c2b1..b5da3e6 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -325,8 +325,11 @@
   
   const Type *OrigTy = V->getType();
   
-  // If this is an extension from the dest type, we can eliminate it.
-  if ((isa<ZExtInst>(I) || isa<SExtInst>(I)) && 
+  // If this is an extension from the dest type, we can eliminate it, even if it
+  // has multiple uses.
+  // FIXME: This is currently disabled until codegen can handle this without
+  // pessimizing code, PR5997.
+  if (0 && (isa<ZExtInst>(I) || isa<SExtInst>(I)) && 
       I->getOperand(0)->getType() == Ty)
     return true;
 
@@ -606,8 +609,10 @@
   if (!I) return false;
   
   // If the input is a truncate from the destination type, we can trivially
-  // eliminate it.
-  if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
+  // eliminate it, even if it has multiple uses.
+  // FIXME: This is currently disabled until codegen can handle this without
+  // pessimizing code, PR5997.
+  if (0 && isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
     return true;
   
   // We can't extend or shrink something that has multiple uses: doing so would
@@ -853,8 +858,11 @@
   Instruction *I = dyn_cast<Instruction>(V);
   if (!I) return false;
   
-  // If this is a truncate from the dest type, we can trivially eliminate it.
-  if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
+  // If this is a truncate from the dest type, we can trivially eliminate it,
+  // even if it has multiple uses.
+  // FIXME: This is currently disabled until codegen can handle this without
+  // pessimizing code, PR5997.
+  if (0 && isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
     return true;
   
   // We can't extend or shrink something that has multiple uses: doing so would