use error returns to generate detailed error messages in the IR checker

compiler/optimizer.go

@@ -25,7 +25,10 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) erro
 
 	// run a check of all of our code
 	if c.VerifyIR {
-		c.checkModule()
+		err := c.checkModule()
+		if err != nil {
+			return err
+		}
 	}
 
 	// Run function passes for each function.
@@ -93,6 +96,11 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) erro
 			return err
 		}
 	}
+	if c.VerifyIR {
+		if err := c.checkModule(); err != nil {
+			return err
+		}
+	}
 	if err := c.Verify(); err != nil {
 		return errors.New("optimizations caused a verification failure")
 	}