compiler: move ReplacePanicsWithTrap pass to transforms

This moves the transformation pass to the right location, and adds tests
to see that it actually works correctly.

compiler/optimizer.go

@@ -20,7 +20,7 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) erro
 	builder.AddCoroutinePassesToExtensionPoints()
 
 	if c.PanicStrategy() == "trap" {
-		c.replacePanicsWithTrap() // -panic=trap
+		transform.ReplacePanicsWithTrap(c.mod) // -panic=trap
 	}
 
 	// run a check of all of our code
@@ -147,22 +147,3 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) erro
 
 	return nil
 }
-
-// Replace panic calls with calls to llvm.trap, to reduce code size. This is the
-// -panic=trap intrinsic.
-func (c *Compiler) replacePanicsWithTrap() {
-	trap := c.mod.NamedFunction("llvm.trap")
-	for _, name := range []string{"runtime._panic", "runtime.runtimePanic"} {
-		fn := c.mod.NamedFunction(name)
-		if fn.IsNil() {
-			continue
-		}
-		for _, use := range getUses(fn) {
-			if use.IsACallInst().IsNil() || use.CalledValue() != fn {
-				panic("expected use of a panic function to be a call")
-			}
-			c.builder.SetInsertPointBefore(use)
-			c.builder.CreateCall(trap, nil, "")
-		}
-	}
-}