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Allow /D flags absent during PCH creation under msvc-compat

Authored by zahen on Jan 14 2020, 2:58 PM.

Description

Allow /D flags absent during PCH creation under msvc-compat

Summary:
Before this patch adding a new /D flag when compiling a source file that consumed a PCH with clang-cl would issue a diagnostic and then fail. With the patch, the diagnostic is still issued but the definition is accepted. This matches the msvc behavior. The fuzzy-pch-msvc.c is a clone of the existing fuzzy-pch.c tests with some msvc specific rework.

msvc diagnostic:

warning C4605: '/DBAR=int' specified on current command line, but was not specified when precompiled header was built

Output of the CHECK-BAR test prior to the code change:

<built-in>(1,9): warning: definition of macro 'BAR' does not match definition in precompiled header [-Wclang-cl-pch]
#define BAR int
        ^
D:\repos\llvm\llvm-project\clang\test\PCH\fuzzy-pch-msvc.c(12,1): error: unknown type name 'BAR'
BAR bar = 17;
^
D:\repos\llvm\llvm-project\clang\test\PCH\fuzzy-pch-msvc.c(23,4): error: BAR was not defined
#  error BAR was not defined
   ^
1 warning and 2 errors generated.

Reviewers: rnk, thakis, hans, zturner

Subscribers: mikerice, aganea, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D72405

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