make instcombine only rewrite a chain of computation

(eliminating some extends) if the new type of the
computation is legal or if both the source and dest
are illegal.  This prevents instcombine from changing big
chains of computation into i64 on 32-bit targets for 
example.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86398 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 19 deletions

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 9d179aea67..74d0971b42 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -8289,23 +8289,6 @@ Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) {
   return commonCastTransforms(CI);
 }
 
-/// isSafeIntegerType - Return true if this is a basic integer type, not a crazy
-/// type like i42.  We don't want to introduce operations on random non-legal
-/// integer types where they don't already exist in the code.  In the future,
-/// we should consider making this based off target-data, so that 32-bit targets
-/// won't get i64 operations etc.
-static bool isSafeIntegerType(const Type *Ty) {
-  switch (Ty->getPrimitiveSizeInBits()) {
-  case 8:
-  case 16:
-  case 32:
-  case 64:
-    return true;
-  default: 
-    return false;
-  }
-}
-
 /// commonIntCastTransforms - This function implements the common transforms
 /// for trunc, zext, and sext.
 Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) {
@@ -8334,8 +8317,10 @@ Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) {
   // Only do this if the dest type is a simple type, don't convert the
   // expression tree to something weird like i93 unless the source is also
   // strange.
-  if ((isSafeIntegerType(DestTy->getScalarType()) ||
-       !isSafeIntegerType(SrcI->getType()->getScalarType())) &&
+  if (TD &&
+      (TD->isLegalInteger(DestTy->getScalarType()->getPrimitiveSizeInBits()) ||
+       !TD->isLegalInteger((SrcI->getType()->getScalarType()
+                            ->getPrimitiveSizeInBits()))) &&
       CanEvaluateInDifferentType(SrcI, DestTy,
                                  CI.getOpcode(), NumCastsRemoved)) {
     // If this cast is a truncate, evaluting in a different type always
@@ -8356,6 +8341,7 @@ Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) {
       break;
     case Instruction::ZExt: {
       DoXForm = NumCastsRemoved >= 1;
+      
       if (!DoXForm && 0) {
         // If it's unnecessary to issue an AND to clear the high bits, it's
         // always profitable to do this xform.