Optimize if range check to replace jumps to bit operation (#87656)

Co-authored-by: Julie Lee <jeonlee@microsoft.com>
Co-authored-by: EgorBo <egorbo@gmail.com>

src/coreclr/jit/CMakeLists.txt

@@ -151,6 +151,7 @@ set( JIT_SOURCES
   objectalloc.cpp
   optcse.cpp
   optimizebools.cpp
+  switchrecognition.cpp
   optimizer.cpp
   patchpoint.cpp
   phase.cpp

src/coreclr/jit/block.cpp

@@ -792,9 +792,6 @@ bool BasicBlock::IsLIR() const
 //------------------------------------------------------------------------
 // firstStmt: Returns the first statement in the block
 //
-// Arguments:
-//    None.
-//
 // Return Value:
 //    The first statement in the block's bbStmtList.
 //
@@ -804,10 +801,18 @@ Statement* BasicBlock::firstStmt() const
 }
 
 //------------------------------------------------------------------------
-// lastStmt: Returns the last statement in the block
+// hasSingleStmt: Returns true if block has a single statement
 //
-// Arguments:
-//    None.
+// Return Value:
+//    true if block has a single statement, false otherwise
+//
+bool BasicBlock::hasSingleStmt() const
+{
+    return (firstStmt() != nullptr) && (firstStmt() == lastStmt());
+}
+
+//------------------------------------------------------------------------
+// lastStmt: Returns the last statement in the block
 //
 // Return Value:
 //    The last statement in the block's bbStmtList.

src/coreclr/jit/block.h

@@ -1127,6 +1127,7 @@ struct BasicBlock : private LIR::Range
 
     Statement* firstStmt() const;
     Statement* lastStmt() const;
+    bool       hasSingleStmt() const;
 
     // Statements: convenience method for enabling range-based `for` iteration over the statement list, e.g.:
     //    for (Statement* const stmt : block->Statements())

src/coreclr/jit/compiler.cpp

@@ -5053,6 +5053,10 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
         // Optimize block order
         //
         DoPhase(this, PHASE_OPTIMIZE_LAYOUT, &Compiler::optOptimizeLayout);
+
+        // Conditional to Switch conversion
+        //
+        DoPhase(this, PHASE_SWITCH_RECOGNITION, &Compiler::optSwitchRecognition);
     }
 
     // Determine start of cold region if we are hot/cold splitting

src/coreclr/jit/compiler.h

@@ -6325,8 +6325,10 @@ class Compiler
 
 public:
     PhaseStatus optOptimizeBools();
+    PhaseStatus optSwitchRecognition();
+    bool optSwitchConvert(BasicBlock* firstBlock, int testsCount, ssize_t* testValues, GenTree* nodeToTest);
+    bool optSwitchDetectAndConvert(BasicBlock* firstBlock);
 
-public:
     PhaseStatus optInvertLoops();    // Invert loops so they're entered at top and tested at bottom.
     PhaseStatus optOptimizeFlow();   // Simplify flow graph and do tail duplication
     PhaseStatus optOptimizeLayout(); // Optimize the BasicBlock layout of the method

src/coreclr/jit/compphases.h

@@ -72,6 +72,7 @@ CompPhaseNameMacro(PHASE_MORPH_MDARR,                "Morph array ops",
 CompPhaseNameMacro(PHASE_HOIST_LOOP_CODE,            "Hoist loop code",                false, -1, false)
 CompPhaseNameMacro(PHASE_MARK_LOCAL_VARS,            "Mark local vars",                false, -1, false)
 CompPhaseNameMacro(PHASE_OPTIMIZE_BOOLS,             "Optimize bools",                 false, -1, false)
+CompPhaseNameMacro(PHASE_SWITCH_RECOGNITION,         "Recognize Switch",               false, -1, false)
 CompPhaseNameMacro(PHASE_FIND_OPER_ORDER,            "Find oper order",                false, -1, false)
 CompPhaseNameMacro(PHASE_SET_BLOCK_ORDER,            "Set block order",                false, -1, true)
 CompPhaseNameMacro(PHASE_BUILD_SSA,                  "Build SSA representation",       true,  -1, false)