[llvm-commits] [llvm] r93200 - /llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp

[Chris Lattner]

Author: lattner
Date: Mon Jan 11 16:45:25 2010
New Revision: 93200

URL: http://llvm.org/viewvc/llvm-project?rev=93200&view=rev
Log:
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%.

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=93200&r1=93199&r2=93200&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Mon Jan 11 16:45:25 2010
@@ -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