Implement -dword-hex-literals

Provide flag for showing showing Word# and Word64# as hexadecimal when
dumping GHC core.  The only affects Word, not Int, and it prefixes the
hexadecimal with enough zeroes to make the total character count a power
of two. For example:

- 0x0C0C instead of 0xC0C
- 0x00BA00BA instead of 0xBA00BA

This also affects the presentation of Word# and Word64# in GHC's error
messages. It is not expected that the flag will be used for this, but
it is a side-effect worth noting.

Test Plan: none

Reviewers: bgamari, simonpj

Reviewed By: simonpj

Subscribers: simonpj, mpickering, rwbarton, thomie, carter, andrewthad

GHC Trac Issues: #14872

Differential Revision: https://phabricator.haskell.org/D4465

1 files changed, 14 insertions, 0 deletions

diff --git a/docs/users_guide/debugging.rst b/docs/users_guide/debugging.rst
index d11cc04fd0..c6d90e642d 100644
--- a/docs/users_guide/debugging.rst
+++ b/docs/users_guide/debugging.rst
@@ -588,6 +588,20 @@ Formatting dumps
     let expressions. This is helpful when your code does a lot of
     unboxing.
 
+.. ghc-flag:: -dhex-word-literals
+    :shortdesc: Print values of type `Word#` in hexadecimal.
+    :type: dynamic
+
+    Print values of type `Word#` and `Word64#` (but not values of
+    type `Int#` and `Int64#`) in hexadecimal instead of decimal.
+    The hexadecimal is zero-padded to make the length of the
+    representation a power of two. For example: `0x0A0A##`,
+    `0x000FFFFF##`, `0xC##`. This flag may be helpful when you
+    are producing a bit pattern that to expect to work correctly on a 32-bit
+    or a 64-bit architecture. Dumping hexadecimal literals after
+    optimizations and constant folding makes it easier to confirm
+    that the generated bit pattern is correct.
+
 .. ghc-flag:: -dno-debug-output
     :shortdesc: Suppress unsolicited debugging output
     :type: dynamic