[SYCL] Disable createIndVarSimplifyPass for SPIR target in SYCL mode. (#2275)

Author: bader

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4106,6 +4106,11 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     if (!Args.hasFlag(options::OPT_fsycl_std_optimizations,
                       options::OPT_fno_sycl_std_optimizations, true))
       CmdArgs.push_back("-fno-sycl-std-optimizations");
+    else if (RawTriple.isSPIR()) {
+      // Set `sycl-opt` option to configure LLVM passes for SPIR target
+      CmdArgs.push_back("-mllvm");
+      CmdArgs.push_back("-sycl-opt");
+    }
 
     // Pass the triple of host when doing SYCL
     auto AuxT = llvm::Triple(llvm::sys::getProcessTriple());

llvm/lib/Transforms/IPO/PassManagerBuilder.cpp

@@ -68,6 +68,10 @@ static cl::opt<bool>
 RunLoopRerolling("reroll-loops", cl::Hidden,
                  cl::desc("Run the loop rerolling pass"));
 
+static cl::opt<bool>
+    SYCLOptimizationMode("sycl-opt", cl::init(false), cl::Hidden,
+                         cl::desc("Enable SYCL optimization mode."));
+
 static cl::opt<bool> RunNewGVN("enable-newgvn", cl::init(false), cl::Hidden,
                                cl::desc("Run the NewGVN pass"));
 
@@ -429,7 +433,12 @@ void PassManagerBuilder::addFunctionSimplificationPasses(
   MPM.add(createCFGSimplificationPass());
   MPM.add(createInstructionCombiningPass());
   // We resume loop passes creating a second loop pipeline here.
-  MPM.add(createIndVarSimplifyPass());        // Canonicalize indvars
+  // TODO: this pass hurts performance due to promotions of induction variables
+  // from 32-bit value to 64-bit values. I assume it's because SPIR is a virtual
+  // target with unlimited # of registers and pass doesn't take into account
+  // that on real HW this promotion is not beneficial.
+  if (!SYCLOptimizationMode)
+    MPM.add(createIndVarSimplifyPass());      // Canonicalize indvars
   MPM.add(createLoopIdiomPass());             // Recognize idioms like memset.
   addExtensionsToPM(EP_LateLoopOptimizations, MPM);
   MPM.add(createLoopDeletionPass());          // Delete dead loops