Try again.

Instead of loading small global string from memory, use
integer constant.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43148 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 29223daab7a8f563f22a380d006837aeabd0b63c..fb7b8d881d76b27b161934d358fba3ab3246fd85 100644 (file)
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -8941,10 +8941,43 @@ Instruction *InstCombiner::visitFreeInst(FreeInst &FI) {
 
 
 /// InstCombineLoadCast - Fold 'load (cast P)' -> cast (load P)' when possible.
-static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI) {
+static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI,
+                                       const TargetData *TD) {
   User *CI = cast<User>(LI.getOperand(0));
   Value *CastOp = CI->getOperand(0);
 
+  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(CI)) {
+    // Instead of loading constant c string, use corresponding integer value
+    // directly if string length is small enough.
+    const std::string &Str = CE->getOperand(0)->getStringValue();
+    if (!Str.empty()) {
+      unsigned len = Str.length();
+      const Type *Ty = cast<PointerType>(CE->getType())->getElementType();
+      unsigned numBits = Ty->getPrimitiveSizeInBits();
+      // Replace LI with immediate integer store.
+      if ((numBits >> 3) == len + 1) {
+       APInt StrVal(numBits, 0);
+       APInt SingleChar(numBits, 0);
+       if (TD->isLittleEndian()) {
+         for (signed i = len-1; i >= 0; i--) {
+           SingleChar = (uint64_t) Str[i];
+           StrVal = (StrVal << 8) | SingleChar;
+         }
+       } else {
+         for (unsigned i = 0; i < len; i++) {
+           SingleChar = (uint64_t) Str[i];
+               StrVal = (StrVal << 8) | SingleChar;
+         }
+         // Append NULL at the end.
+         SingleChar = 0;
+         StrVal = (StrVal << 8) | SingleChar;
+       }
+       Value *NL = ConstantInt::get(StrVal);
+       return IC.ReplaceInstUsesWith(LI, NL);
+      }
+    }
+  }
+
   const Type *DestPTy = cast<PointerType>(CI->getType())->getElementType();
   if (const PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType())) {
     const Type *SrcPTy = SrcTy->getElementType();
@@ -9050,7 +9083,7 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
 
   // load (cast X) --> cast (load X) iff safe
   if (isa<CastInst>(Op))
-    if (Instruction *Res = InstCombineLoadCast(*this, LI))
+    if (Instruction *Res = InstCombineLoadCast(*this, LI, TD))
       return Res;
 
   // None of the following transforms are legal for volatile loads.
@@ -9114,7 +9147,7 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
         }
 
       } else if (CE->isCast()) {
-        if (Instruction *Res = InstCombineLoadCast(*this, LI))
+        if (Instruction *Res = InstCombineLoadCast(*this, LI, TD))
           return Res;
       }
   }