[𝘀𝗽𝗿] initial version

Created using spr 1.3.7

Author: boomanaiden154

llvm/test/tools/llvm-exegesis/X86/snippet-generator-seed.test

@@ -0,0 +1,16 @@
+# REQUIRES: exegesis-can-measure-latency, x86_64-linux
+
+# Check that the snippet we generate is exactly the same between runs when we
+# use a fixed RNG seed.
+
+# RUN: llvm-exegesis -mtriple=x86_64-unknown-unknown -mode=latency -opcode-name=ADD64rr --benchmark-phase=prepare-snippet -random-generator-seed=5 | FileCheck %s
+
+# CHECK: ---
+# CHECK: mode:            latency
+# CHECK: key:
+# CHECK:   instructions:
+# CHECK:     - 'ADD64rr RCX RCX RAX'
+# CHECK:   config:          ''
+# CHECK:   register_initial_values:
+# CHECK:     - 'RCX=0x0'
+# CHECK:     - 'RAX=0x0'

llvm/tools/llvm-exegesis/lib/SnippetGenerator.cpp

@@ -21,9 +21,17 @@
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/Program.h"
 
+#define DEBUG_TYPE "snippet-generator"
+
 namespace llvm {
 namespace exegesis {
 
+static cl::opt<unsigned>
+    RandomGeneratorSeed("random-generator-seed",
+                        cl::desc("The seed value to use for the random number "
+                                 "generator when generating snippets."),
+                        cl::init(0));
+
 std::vector<CodeTemplate> getSingleton(CodeTemplate &&CT) {
   std::vector<CodeTemplate> Result;
   Result.push_back(std::move(CT));
@@ -187,8 +195,13 @@ generateUnconstrainedCodeTemplates(const InstructionTemplate &Variant,
 }
 
 std::mt19937 &randomGenerator() {
+  unsigned RandomSeed = RandomGeneratorSeed;
   static std::random_device RandomDevice;
-  static std::mt19937 RandomGenerator(RandomDevice());
+  if (RandomSeed == 0) {
+    RandomSeed = RandomDevice();
+  }
+  LLVM_DEBUG(dbgs() << "Using random seed " << RandomSeed << ".\n");
+  static std::mt19937 RandomGenerator(RandomSeed);
   return RandomGenerator;
 }