Copy Alignment for derived global strings from existing ones

Author: dominik-steenken

llvm/lib/IR/IRBuilder.cpp

@@ -52,7 +52,7 @@ GlobalVariable *IRBuilderBase::CreateGlobalString(StringRef Str,
       *M, StrConstant->getType(), true, GlobalValue::PrivateLinkage,
       StrConstant, Name, nullptr, GlobalVariable::NotThreadLocal, AddressSpace);
   GV->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
-  GV->setAlignment(M->getDataLayout().getPreferredAlign(GV));
+  GV->setAlignment(Align(1));
   return GV;
 }
 

llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp

@@ -24,6 +24,7 @@
 #include "llvm/IR/AttributeMask.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Function.h"
+#include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
@@ -3320,8 +3321,14 @@ Value *LibCallSimplifier::optimizePrintFString(CallInst *CI, IRBuilderBase &B) {
     // printf("%s", str"\n") --> puts(str)
     if (OperandStr.back() == '\n') {
       OperandStr = OperandStr.drop_back();
-      Value *GV = B.CreateGlobalString(OperandStr, "str");
-      return copyFlags(*CI, emitPutS(GV, B, TLI));
+      // Because we were able to derive OperandStr, we know it's safe to cast to
+      // GlobalVariable*.
+      GlobalVariable *OldStr =
+          dyn_cast<GlobalVariable>(getUnderlyingObject(CI->getArgOperand(1)));
+      GlobalVariable *NewStr = B.CreateGlobalString(
+          OperandStr, Twine(OldStr->getName(), ".clipped"));
+      NewStr->setAlignment(OldStr->getAlign());
+      return copyFlags(*CI, emitPutS(NewStr, B, TLI));
     }
     return nullptr;
   }
@@ -3332,8 +3339,14 @@ Value *LibCallSimplifier::optimizePrintFString(CallInst *CI, IRBuilderBase &B) {
     // Create a string literal with no \n on it.  We expect the constant merge
     // pass to be run after this pass, to merge duplicate strings.
     FormatStr = FormatStr.drop_back();
-    Value *GV = B.CreateGlobalString(FormatStr, "str");
-    return copyFlags(*CI, emitPutS(GV, B, TLI));
+    // Because we were able to derive FormatStr, we know it's safe to cast to
+    // GlobalVariable*.
+    GlobalVariable *OldStr =
+        dyn_cast<GlobalVariable>(getUnderlyingObject(CI->getArgOperand(0)));
+    GlobalVariable *NewStr =
+        B.CreateGlobalString(FormatStr, Twine(OldStr->getName(), ".clipped"));
+    NewStr->setAlignment(OldStr->getAlign());
+    return copyFlags(*CI, emitPutS(NewStr, B, TLI));
   }
 
   // Optimize specific format strings.