[PATCH] Have a way to let fast-isel handle normally optimized library functions

[reed kotler]

Hi mcrosier,

For some reason, LLVM decides to not handle functions in the C library that are normally
marked as optimized. I don't know the history of this but for sure in the mips fast-isel port we don't
want this behavior so I have provided a way for a class that is derived from the target independent fast-isel
to override this behavior.

http://reviews.llvm.org/D7397

Files:
  include/llvm/CodeGen/FastISel.h
  lib/CodeGen/SelectionDAG/FastISel.cpp
  lib/Target/Mips/MipsFastISel.cpp
  test/CodeGen/Mips/Fast-ISel/strlen2.ll

Index: include/llvm/CodeGen/FastISel.h
===================================================================
--- include/llvm/CodeGen/FastISel.h
+++ include/llvm/CodeGen/FastISel.h
@@ -199,6 +199,8 @@
   const TargetLibraryInfo *LibInfo;
   bool SkipTargetIndependentISel;
 
+  bool HandleOptimizedCodeGenFunctions;
+
   /// \brief The position of the last instruction for materializing constants
   /// for use in the current block. It resets to EmitStartPt when it makes sense
   /// (for example, it's usually profitable to avoid function calls between the
@@ -535,6 +537,9 @@
   bool selectExtractValue(const User *I);
   bool selectInsertValue(const User *I);
 
+  void setHandleOptimizedCodeGenFunctions(bool Value);
+  bool handleOptimizedCodeGenFunctions();
+
 private:
   /// \brief Handle PHI nodes in successor blocks.
   ///
Index: lib/CodeGen/SelectionDAG/FastISel.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/FastISel.cpp
+++ lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -1311,7 +1311,8 @@
 
     // As a special case, don't handle calls to builtin library functions that
     // may be translated directly to target instructions.
-    if (F && !F->hasLocalLinkage() && F->hasName() &&
+    if (!handleOptimizedCodeGenFunctions() &&
+        F && !F->hasLocalLinkage() && F->hasName() &&
         LibInfo->getLibFunc(F->getName(), Func) &&
         LibInfo->hasOptimizedCodeGen(Func))
       return false;
@@ -1584,7 +1585,8 @@
       TII(*MF->getSubtarget().getInstrInfo()),
       TLI(*MF->getSubtarget().getTargetLowering()),
       TRI(*MF->getSubtarget().getRegisterInfo()), LibInfo(LibInfo),
-      SkipTargetIndependentISel(SkipTargetIndependentISel) {}
+      SkipTargetIndependentISel(SkipTargetIndependentISel),
+      HandleOptimizedCodeGenFunctions(false) {}
 
 FastISel::~FastISel() {}
 
@@ -2185,3 +2187,11 @@
 
   return Predicate;
 }
+
+void FastISel::setHandleOptimizedCodeGenFunctions(bool Value) {
+  HandleOptimizedCodeGenFunctions = Value;
+}
+
+bool FastISel::handleOptimizedCodeGenFunctions() {
+  return HandleOptimizedCodeGenFunctions;
+}
Index: lib/Target/Mips/MipsFastISel.cpp
===================================================================
--- lib/Target/Mips/MipsFastISel.cpp
+++ lib/Target/Mips/MipsFastISel.cpp
@@ -167,6 +167,7 @@
          ((Subtarget->hasMips32r2() || Subtarget->hasMips32()) &&
           (static_cast<const MipsTargetMachine &>(TM).getABI().IsO32())));
     UnsupportedFPMode = Subtarget->isFP64bit();
+    setHandleOptimizedCodeGenFunctions(true);
   }
 
   unsigned fastMaterializeConstant(const Constant *C) override;
Index: test/CodeGen/Mips/Fast-ISel/strlen2.ll
===================================================================
--- /dev/null
+++ test/CodeGen/Mips/Fast-ISel/strlen2.ll
@@ -0,0 +1,21 @@
+; RUN: llc -march=mipsel -relocation-model=pic -O0 -fast-isel -mips-fast-isel -fast-isel-abort -mcpu=mips32r2 \
+; RUN:     < %s | FileCheck %s
+
+ at .str = private unnamed_addr constant [6 x i8] c"hello\00", align 1
+ at hello = global i8* getelementptr inbounds ([6 x i8]* @.str, i32 0, i32 0), align 4
+ at len = common global i32 0, align 4
+
+; Function Attrs: nounwind
+define void @foo()  {
+entry:
+; CHECK: 	.ent	foo
+  %0 = load i8** @hello, align 4
+  %call = call i32 @strlen(i8* %0) #2
+  store i32 %call, i32* @len, align 4
+  ret void
+}
+
+; Function Attrs: nounwind readonly
+declare i32 @strlen(i8*) 
+
+

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