[H2BLB][TPC] Add the simple cst prop pass

Customize the addition of IR passes in our implementation of TargetPassConfig.

This commit adds our custom simple constant propagation pass after all the
standard IR passes.

llvm/lib/Target/H2BLB/H2BLBTargetMachine.cpp

@@ -18,6 +18,7 @@
 #include "llvm/CodeGen/TargetPassConfig.h"
 #include "llvm/MC/TargetRegistry.h" // For RegisterTargetMachine.
 #include "llvm/Passes/PassBuilder.h"
+#include "llvm/Support/CodeGen.h"  // For CodeGenOptLevel.
 #include "llvm/Support/Compiler.h" // For LLVM_EXTERNAL_VISIBILITY.
 #include <memory>
 
@@ -109,3 +110,10 @@ bool H2BLBPassConfig::addInstSelector() {
   // TODO: We need to hook up the DAG selector here.
   return false;
 }
+
+void H2BLBPassConfig::addIRPasses() {
+  // Add the regular IR passes before putting our passes.
+  TargetPassConfig::addIRPasses();
+  if (getOptLevel() != CodeGenOptLevel::None)
+    addPass(createH2BLBSimpleConstantPropagationPassForLegacyPM());
+}

llvm/lib/Target/H2BLB/H2BLBTargetMachine.h

@@ -51,6 +51,7 @@ class H2BLBPassConfig : public TargetPassConfig {
   H2BLBPassConfig(LLVMTargetMachine &TM, PassManagerBase &PM);
 
   bool addInstSelector() override;
+  void addIRPasses() override;
 };
 
 } // end namespace llvm

llvm/test/CodeGen/H2BLB/llc-pipeline.ll

@@ -0,0 +1,10 @@
+; RUN: llc -O0 -mtriple h2blb %s -debug-pass=Structure --stop-before=peephole-opt -o /dev/null 2>&1 | FileCheck %s --check-prefix=CHECK-O0
+; RUN: llc -O1 -mtriple h2blb %s -debug-pass=Structure --stop-before=peephole-opt -o /dev/null 2>&1 | FileCheck %s --check-prefix=CHECK-Opt
+; RUN: llc -O2 -mtriple h2blb %s -debug-pass=Structure --stop-before=peephole-opt -o /dev/null 2>&1 | FileCheck %s --check-prefix=CHECK-Opt
+; RUN: llc -O3 -mtriple h2blb %s -debug-pass=Structure --stop-before=peephole-opt -o /dev/null 2>&1 | FileCheck %s --check-prefix=CHECK-Opt
+
+; Check that the H2BLB custom codegen pipeline includes the target specific
+; simple constant propagation pass, but only when the optimizations are enabled.
+
+; CHECK-O0-NOT: H2BLB simple constant propagation
+; CHECK-Opt: H2BLB simple constant propagation