Do ProgramScopeConstantResolution later in cogeden and add SROA+Instcombine to promote constants

If we still have any unresolved constants in the beginning of the codegen,
we have no change to promote them to immediates after they are lowered to
load/stores from constantBase.
So this change moves ProgramScopeConstantResolution after MemCpy lowering
and adds SROA+InstCombine to promote the constants if it becomes possible
after it.

Author: admitric

IGC/Compiler/CISACodeGen/ShaderCodeGen.cpp

@@ -453,15 +453,6 @@ void AddLegalizationPasses(CodeGenContext& ctx, IGCPassManager& mpm, PSSignature
         mpm.add(llvm::createLoopSimplifyPass());
     }
 
-
-    // Lower/Resolve OCL inlined constants.
-    if (ctx.m_DriverInfo.NeedLoweringInlinedConstants()) {
-        // Run additional constant breaking which is assumed by the constant
-        // resolver.
-        mpm.add(new BreakConstantExpr());
-        mpm.add(new ProgramScopeConstantResolution());
-    }
-
     // This is the condition that double emulation is used.
     ctx.checkDPEmulationEnabled();
 
@@ -532,6 +523,19 @@ void AddLegalizationPasses(CodeGenContext& ctx, IGCPassManager& mpm, PSSignature
     }
 
     mpm.add(createReplaceUnsupportedIntrinsicsPass());
+    // Lowering MemCpy may allow us to promote some program scope constants to immediates.
+    // So adding SROA + InstCombine to eliminate alloca + propagate constants.
+    mpm.add(createSROAPass());
+    mpm.add(createIGCInstructionCombiningPass());
+
+    // Lower/Resolve OCL inlined constants.
+    // Doing it after MemCpy lowering to have the last change to promote them to immediates.
+    if (ctx.m_DriverInfo.NeedLoweringInlinedConstants()) {
+        // Run additional constant breaking which is assumed by the constant
+        // resolver.
+        mpm.add(new BreakConstantExpr());
+        mpm.add(new ProgramScopeConstantResolution());
+    }
 
     if (IGC_IS_FLAG_DISABLED(DisablePromoteToDirectAS) &&
         !ctx.getModuleMetaData()->compOpt.IsLibraryCompilation)