Add simple Else conditions to If Conversion (#77728)

* Add simple Else conditions to If Conversion

For example:
if (x < 7) { a = 5; } else { a = 9; }
a = (cond) ? b : c;

The else condition must write to the same variable as the then
statement.

* Move phase and stop updating ssa

* Wrap JitConfig access

* Add GT_RETURN else cases

* Add test cases with verification checks

* Ensure single only operation condition checks are used

* Remove empty line

* Use DOTNET_ instead of COMPlus_

* Move JitDoIfConversion check

* Move if conversion into it's own file

* Always invert condition

* Rename IfConvertMergeBlocks

* Use gtGetOp1()

* Expand tests

* Add operation type assert

* Allow nested SELECT nodes

* Fix condition directions

Author: a74nh

src/coreclr/jit/CMakeLists.txt

@@ -124,6 +124,7 @@ set( JIT_SOURCES
   hashbv.cpp
   hwintrinsic.cpp
   hostallocator.cpp
+  ifconversion.cpp
   indirectcalltransformer.cpp
   importercalls.cpp
   importer.cpp

src/coreclr/jit/compiler.cpp

@@ -4755,7 +4755,6 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
         bool doCse                     = true;
         bool doAssertionProp           = true;
         bool doRangeAnalysis           = true;
-        bool doIfConversion            = true;
         bool doVNBasedDeadStoreRemoval = true;
         int  iterations                = 1;
 
@@ -4769,7 +4768,6 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
         doCse                     = doValueNum;
         doAssertionProp           = doValueNum && (JitConfig.JitDoAssertionProp() != 0);
         doRangeAnalysis           = doAssertionProp && (JitConfig.JitDoRangeAnalysis() != 0);
-        doIfConversion            = doIfConversion && (JitConfig.JitDoIfConversion() != 0);
         doVNBasedDeadStoreRemoval = doValueNum && (JitConfig.JitDoVNBasedDeadStoreRemoval() != 0);
 
         if (opts.optRepeat)
@@ -4852,13 +4850,6 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
                 DoPhase(this, PHASE_ASSERTION_PROP_MAIN, &Compiler::optAssertionPropMain);
             }
 
-            if (doIfConversion)
-            {
-                // If conversion
-                //
-                DoPhase(this, PHASE_IF_CONVERSION, &Compiler::optIfConversion);
-            }
-
             if (doRangeAnalysis)
             {
                 // Bounds check elimination via range analysis
@@ -4910,6 +4901,10 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
         //
         DoPhase(this, PHASE_OPTIMIZE_BOOLS, &Compiler::optOptimizeBools);
 
+        // If conversion
+        //
+        DoPhase(this, PHASE_IF_CONVERSION, &Compiler::optIfConversion);
+
         // Optimize block order
         //
         DoPhase(this, PHASE_OPTIMIZE_LAYOUT, &Compiler::optOptimizeLayout);