[llvm-mca] Add a -mattr flag

[dmgreen]

Summary

This adds a -mattr flag to llvm-mca, for cases where the -mcpu option does not contain all optional features.

[andreadb]

LGTM

Thanks!

llvm/test/tools/llvm-mca/ARM/m4-targetfeatures.s

+# NOTE: Assertions have been autogenerated by utils/update_mca_test_checks.py
+# RUN: llvm-mca -mtriple=arm-none-none-eabi -mcpu=cortex-m4 -mattr=+fp64 -instruction-tables < %s | FileCheck %s
+
+vadd.f32 s0, s2, s2
+vadd.f64 d0, d2, d2
+
+# CHECK:      Instruction Info:
+# CHECK-NEXT: [1]: #uOps
+# CHECK-NEXT: [2]: Latency
+# CHECK-NEXT: [3]: RThroughput
+# CHECK-NEXT: [4]: MayLoad
+# CHECK-NEXT: [5]: MayStore
+# CHECK-NEXT: [6]: HasSideEffects (U)
+
+# CHECK:      [1]    [2]    [3]    [4]    [5]    [6]    Instructions:
+# CHECK-NEXT:  1      1     1.00                        vadd.f32  s0, s2, s2
+# CHECK-NEXT:  1      1     1.00                        vadd.f64  d0, d2, d2
+
+# CHECK:      Resources:
+# CHECK-NEXT: [0]   - M4Unit
+
+# CHECK:      Resource pressure per iteration:
+# CHECK-NEXT: [0]
+# CHECK-NEXT: 2.00
+
+# CHECK:      Resource pressure by instruction:
+# CHECK-NEXT: [0]    Instructions:
+# CHECK-NEXT: 1.00   vadd.f32 s0, s2, s2
+# CHECK-NEXT: 1.00   vadd.f64 d0, d2, d2

llvm/tools/llvm-mca/llvm-mca.cpp

TripleName("mtriple",
                cl::desc("Target triple. See -version for available targets"),
                cl::cat(ToolOptions));
 
 static cl::opt<std::string>
     MCPU("mcpu",
          cl::desc("Target a specific cpu type (-mcpu=help for details)"),
          cl::value_desc("cpu-name"), cl::cat(ToolOptions), cl::init("native"));
 
+static cl::opt<std::string>
+    MATTR("mattr",
+          cl::desc("Additional target features."),
+          cl::cat(ToolOptions));
+
 static cl::opt<int>
     OutputAsmVariant("output-asm-variant",
                      cl::desc("Syntax variant to use for output printing"),
                      cl::cat(ToolOptions), cl::init(-1));
 
 static cl::opt<bool>
     PrintImmHex("print-imm-hex", cl::cat(ToolOptions), cl::init(false),
                 cl::desc("Prefer hex format when printing immediate values"));
int main(int argc, char **argv) {
 
   // Apply overrides to llvm-mca specific options.
   processViewOptions();
 
   if (!MCPU.compare("native"))
     MCPU = llvm::sys::getHostCPUName();
 
   std::unique_ptr<MCSubtargetInfo> STI(
-      TheTarget->createMCSubtargetInfo(TripleName, MCPU, /* FeaturesStr */ ""));
+      TheTarget->createMCSubtargetInfo(TripleName, MCPU, MATTR));
   if (!STI->isCPUStringValid(MCPU))
     return 1;
 
   if (!PrintInstructionTables && !STI->getSchedModel().isOutOfOrder()) {
     WithColor::error() << "please specify an out-of-order cpu. '" << MCPU
                        << "' is an in-order cpu.\n";
     return 1;
   }