add STRESS_PROMOTE_LESS_STRUCTS mode. (#49084)

* add STRESS_PROMOTE_LESS_STRUCTS mode.

* add comment

* Disable failing tests.

* review

* fix build break

src/coreclr/jit/compiler.cpp

@@ -3594,6 +3594,31 @@ bool Compiler::compStressCompileHelper(compStressArea stressArea, unsigned weigh
     return (hash < weight);
 }
 
+//------------------------------------------------------------------------
+// compPromoteFewerStructs: helper to determine if the local
+//   should not be promoted under a stress mode.
+//
+// Arguments:
+//   lclNum - local number to test
+//
+// Returns:
+//   true if this local should not be promoted.
+//
+// Notes:
+//   Reject ~50% of the potential promotions if STRESS_PROMOTE_FEWER_STRUCTS is active.
+//
+bool Compiler::compPromoteFewerStructs(unsigned lclNum)
+{
+    bool       rejectThisPromo = false;
+    const bool promoteLess     = compStressCompile(STRESS_PROMOTE_FEWER_STRUCTS, 50);
+    if (promoteLess)
+    {
+
+        rejectThisPromo = (((info.compMethodHash() ^ lclNum) & 1) == 0);
+    }
+    return rejectThisPromo;
+}
+
 #endif // DEBUG
 
 void Compiler::compInitDebuggingInfo()

src/coreclr/jit/compiler.h

@@ -9268,6 +9268,7 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
         STRESS_MODE(GENERIC_VARN)                                                               \
         STRESS_MODE(PROFILER_CALLBACKS) /* Will generate profiler hooks for ELT callbacks */    \
         STRESS_MODE(BYREF_PROMOTION) /* Change undoPromotion decisions for byrefs */            \
+        STRESS_MODE(PROMOTE_FEWER_STRUCTS)/* Don't promote some structs that can be promoted */ \
                                                                                                 \
         /* After COUNT_VARN, stress level 2 does all of these all the time */                   \
                                                                                                 \
@@ -9314,6 +9315,8 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
         return compStressCompile(STRESS_RANDOM_INLINE, 50);
     }
 
+    bool compPromoteFewerStructs(unsigned lclNum);
+
 #endif // DEBUG
 
     bool compTailCallStress()

src/coreclr/jit/lclvars.cpp

@@ -2104,6 +2104,14 @@ bool Compiler::StructPromotionHelper::ShouldPromoteStructVar(unsigned lclNum)
         // TODO-1stClassStructs: a temporary solution to keep diffs small, it will be fixed later.
         shouldPromote = false;
     }
+#if defined(DEBUG)
+    else if (compiler->compPromoteFewerStructs(lclNum))
+    {
+        // Do not promote some structs, that can be promoted, to stress promoted/unpromoted moves.
+        JITDUMP("Not promoting promotable struct local V%02u, because of STRESS_PROMOTE_FEWER_STRUCTS\n", lclNum);
+        shouldPromote = false;
+    }
+#endif
 
     //
     // If the lvRefCnt is zero and we have a struct promoted parameter we can end up with an extra store of

src/tests/Interop/PInvoke/Vector2_3_4/Vector2_3_4.csproj

@@ -1,6 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
+    <!-- https://github.com/dotnet/runtime/issues/49189 -->
+    <JitOptimizationSensitive Condition="'$(TargetArchitecture)' == 'x86'">true</JitOptimizationSensitive>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="*.cs" />

src/tests/JIT/Methodical/xxobj/ldobj/_il_relldobj_V.ilproj

@@ -2,6 +2,8 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <CLRTestPriority>1</CLRTestPriority>
+    <!-- https://github.com/dotnet/runtime/issues/49189 -->
+    <JitOptimizationSensitive Condition="'$(TargetArchitecture)' == 'x86'">true</JitOptimizationSensitive>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>PdbOnly</DebugType>