[X86] Reduce memory allocations in X86TargetMachine::getSubtargetImpl

We performed a number of memory allocations each time getTTI was called,
remove them by using SmallString.
No functionality change intended.

llvm-svn: 270246

1 files changed, 12 insertions, 7 deletions

diff --git a/llvm/lib/Target/X86/X86TargetMachine.cpp b/llvm/lib/Target/X86/X86TargetMachine.cpp
index 3ff847a..31918d0 100644
--- a/llvm/lib/Target/X86/X86TargetMachine.cpp
+++ b/llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -182,12 +182,12 @@ X86TargetMachine::getSubtargetImpl(const Function &F) const {
   Attribute CPUAttr = F.getFnAttribute("target-cpu");
   Attribute FSAttr = F.getFnAttribute("target-features");
 
-  std::string CPU = !CPUAttr.hasAttribute(Attribute::None)
-                        ? CPUAttr.getValueAsString().str()
-                        : TargetCPU;
-  std::string FS = !FSAttr.hasAttribute(Attribute::None)
-                       ? FSAttr.getValueAsString().str()
-                       : TargetFS;
+  SmallString<32> CPU = !CPUAttr.hasAttribute(Attribute::None)
+                            ? CPUAttr.getValueAsString()
+                            : (StringRef)TargetCPU;
+  SmallString<512> FS = !FSAttr.hasAttribute(Attribute::None)
+                            ? FSAttr.getValueAsString()
+                            : (StringRef)TargetFS;
 
   // FIXME: This is related to the code below to reset the target options,
   // we need to know whether or not the soft float flag is set on the
@@ -201,7 +201,12 @@ X86TargetMachine::getSubtargetImpl(const Function &F) const {
   if (SoftFloat)
     FS += FS.empty() ? "+soft-float" : ",+soft-float";
 
-  auto &I = SubtargetMap[CPU + FS];
+  SmallString<544> Key;
+  Key.reserve(CPU.size() + FS.size());
+  Key += CPU;
+  Key += FS;
+
+  auto &I = SubtargetMap[Key];
   if (!I) {
     // This needs to be done before we create a new subtarget since any
     // creation will depend on the TM and the code generation flags on the