[Hexagon] Emit jump tables in text section based on a flag

[sgundapa]

Summary

This patch adds a new LLVM flag -hexagon-emit-jt-text which is defaulted to
"false". The value "true" emits the switch generated jump tables in text section.

lib/Target/Hexagon/HexagonTargetObjectFile.h

bool isGlobalInSmallSection(const GlobalObject *GO,
                                 const TargetMachine &TM) const;
 
     bool isSmallDataEnabled() const;
 
     unsigned getSmallDataSize() const;
 
     const Function *getLutUsedFunction(const GlobalObject *GO) const;
 
+    bool shouldPutJumpTableInFunctionSection(bool UsesLabelDifference,
+                                             const Function &F) const override;
+
   private:
     MCSectionELF *SmallDataSection;
     MCSectionELF *SmallBSSSection;
 
     unsigned getSmallestAddressableSize(const Type *Ty, const GlobalValue *GV,
         const TargetMachine &TM) const;
 
     MCSection *selectSmallSectionForGlobal(const GlobalObject *GO,

lib/Target/Hexagon/HexagonTargetObjectFile.cpp

 static cl::opt<bool> TraceGVPlacement("trace-gv-placement",
   cl::Hidden, cl::init(false),
   cl::desc("Trace global value placement"));
 
 static cl::opt<bool>
     EmitLutInText("hexagon-emit-lut-text", cl::Hidden, cl::init(false),
                  cl::desc("Emit hexagon lookup tables in function section"));
 
+static cl::opt<bool>
+    EmitJtInText("hexagon-emit-jt-text", cl::Hidden, cl::init(false),
+                 cl::desc("Emit hexagon jump tables in function section"));
+
 // TraceGVPlacement controls messages for all builds. For builds with assertions
 // (debug or release), messages are also controlled by the usual debug flags
 // (e.g. -debug and -debug-only=globallayout)
 #define TRACE_TO(s, X) s << X
 #ifdef NDEBUG
 #define TRACE(X)                                                               \
   do {                                                                         \
     if (TraceGVPlacement) {                                                    \

 bool HexagonTargetObjectFile::isSmallDataEnabled() const {
   return SmallDataThreshold > 0;
 }
 
 unsigned HexagonTargetObjectFile::getSmallDataSize() const {
   return SmallDataThreshold;
 }
 
+bool HexagonTargetObjectFile::shouldPutJumpTableInFunctionSection(
+    bool UsesLabelDifference, const Function &F) const {
+  return EmitJtInText;
+}
+
 /// Descends any type down to "elementary" components,
 /// discovering the smallest addressable one.
 /// If zero is returned, declaration will not be modified.
 unsigned HexagonTargetObjectFile::getSmallestAddressableSize(const Type *Ty,
       const GlobalValue *GV, const TargetMachine &TM) const {
   // Assign the smallest element access size to the highest
   // value which assembler can handle.
   unsigned SmallestElement = 8;

test/CodeGen/Hexagon/jt-in-text.ll

+; RUN: llc -hexagon-emit-jt-text=true < %s | FileCheck %s
+target datalayout = "e-m:e-p:32:32:32-a:0-n16:32-i64:64:64-i32:32:32-i16:16:16-i1:8:8-f32:32:32-f64:64:64-v32:32:32-v64:64:64-v512:512:512-v1024:1024:1024-v2048:2048:2048"
+target triple = "hexagon-unknown--elf"
+
+; CHECK: .text
+; CHECK-NOT: .rodata
+; CHECK: .word
+
+@lane0_pwr_st = global i32 0, align 4
+@lane1_pwr_st = global i32 0, align 4
+@lane2_pwr_st = global i32 0, align 4
+@lane3_pwr_st = global i32 0, align 4
+
+; Function Attrs: noinline nounwind
+define void @test2(i32 %lane_id, i32 %rx_pwr_st) #0 {
+entry:
+  %lane_id.addr = alloca i32, align 4
+  %rx_pwr_st.addr = alloca i32, align 4
+  store i32 %lane_id, i32* %lane_id.addr, align 4
+  store i32 %rx_pwr_st, i32* %rx_pwr_st.addr, align 4
+  %0 = load i32, i32* %lane_id.addr, align 4
+  switch i32 %0, label %sw.epilog [
+    i32 0, label %sw.bb
+    i32 1, label %sw.bb1
+    i32 2, label %sw.bb2
+    i32 3, label %sw.bb3
+    i32 15, label %sw.bb4
+  ]
+
+sw.bb:                                            ; preds = %entry
+  store i32 1, i32* @lane0_pwr_st, align 4
+  br label %sw.epilog
+
+sw.bb1:                                           ; preds = %entry
+  store i32 1, i32* @lane1_pwr_st, align 4
+  br label %sw.epilog
+
+sw.bb2:                                           ; preds = %entry
+  store i32 1, i32* @lane2_pwr_st, align 4
+  br label %sw.epilog
+
+sw.bb3:                                           ; preds = %entry
+  store i32 1, i32* @lane3_pwr_st, align 4
+  br label %sw.epilog
+
+sw.bb4:                                           ; preds = %entry
+  store i32 1, i32* @lane0_pwr_st, align 4
+  store i32 1, i32* @lane1_pwr_st, align 4
+  store i32 1, i32* @lane2_pwr_st, align 4
+  store i32 1, i32* @lane3_pwr_st, align 4
+  br label %sw.epilog
+
+sw.epilog:                                        ; preds = %entry, %sw.bb4, %sw.bb3, %sw.bb2, %sw.bb1, %sw.bb
+  ret void
+}
+
+attributes #0 = { noinline nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="hexagonv60" "target-features"="-hvx-double,-long-calls" "unsafe-fp-math"="false" "use-soft-float"="false" }