GlobalISel: Trivial documentation and comment fixes

Differential Revision: https://reviews.llvm.org/D124808

Author: nhaehnle

llvm/docs/GlobalISel/GenericOpcode.rst

@@ -405,8 +405,8 @@ normal input. Also produce a carry output in addition to the normal result.
 G_UMULH, G_SMULH
 ^^^^^^^^^^^^^^^^
 
-Multiply two numbers at twice the incoming bit width (signed) and return
-the high half of the result.
+Multiply two numbers at twice the incoming bit width (unsigned or signed) and
+return the high half of the result.
 
 .. code-block:: none
 

llvm/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h

@@ -1449,8 +1449,8 @@ class MachineIRBuilder {
 
   /// Build and insert \p Res = G_SUB \p Op0, \p Op1
   ///
-  /// G_SUB sets \p Res to the sum of integer parameters \p Op0 and \p Op1,
-  /// truncated to their width.
+  /// G_SUB sets \p Res to the difference of integer parameters \p Op0 and
+  /// \p Op1, truncated to their width.
   ///
   /// \pre setBasicBlock or setMI must have been called.
   /// \pre \p Res, \p Op0 and \p Op1 must be generic virtual registers
@@ -1466,7 +1466,7 @@ class MachineIRBuilder {
 
   /// Build and insert \p Res = G_MUL \p Op0, \p Op1
   ///
-  /// G_MUL sets \p Res to the sum of integer parameters \p Op0 and \p Op1,
+  /// G_MUL sets \p Res to the product of integer parameters \p Op0 and \p Op1,
   /// truncated to their width.
   ///
   /// \pre setBasicBlock or setMI must have been called.