[flang] Use precompiled headers in Lower, Parser and Semantics

Precompiling larger headers can save a lot of compile time across
various compilation units.

Selected compile time & memory improvements are as follows:

flang/lib/Parser/Fortran-parsers.cpp:
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:47.31 -> 0:41.68
Maximum resident set size (kbytes): 2062140 -> 1745584

flang/lib/Lower/Bridge.cpp:
Elapsed (wall clock) time (h:mm:ss or m:ss): 1:19.16 -> 0:45.86
Maximum resident set size (kbytes): 3849144 -> 2443476

flang/lib/Lower/PFTBuilder.cpp
Elapsed (wall clock) time (h:mm:ss or m:ss): 1:29.24 -> 1:00.99
Maximum resident set size (kbytes): 4218368 -> 2923128

flang/lib/Lower/Allocatable.cpp
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:53.03 -> 0:22.50
Maximum resident set size (kbytes): 3092840 -> 2116908

flang/lib/Semantics/Semantics.cpp
Elapsed (wall clock) time (h:mm:ss or m:ss): 1:18.75 -> 1:00.20
Maximum resident set size (kbytes): 3527744 -> 2545308

While the newly added precompiled headers are as follows:

Parser:
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:09.62
Maximum resident set size (kbytes): 1034608

Lower:
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:41.33
Maximum resident set size (kbytes): 3615240

Semantics:
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:26.69
Maximum resident set size (kbytes): 2403776

Signed-off-by: Kajetan Puchalski <[email protected]>

Author: mrkajetanp

flang/lib/Lower/CMakeLists.txt

@@ -73,3 +73,14 @@ add_flang_library(FortranLower
   MLIRLLVMDialect
   MLIRSCFToControlFlow
 )
+
+target_precompile_headers(FortranLower PRIVATE
+  [["flang/Lower/ConvertExpr.h"]]
+  [["flang/Lower/SymbolMap.h"]]
+  [["flang/Lower/AbstractConverter.h"]]
+  [["flang/Lower/IterationSpace.h"]]
+  [["flang/Lower/CallInterface.h"]]
+  [["flang/Lower/BoxAnalyzer.h"]]
+  [["flang/Lower/PFTBuilder.h"]]
+  [["flang/Lower/DirectivesCommon.h"]]
+)

flang/lib/Parser/CMakeLists.txt

@@ -36,3 +36,11 @@ add_flang_library(FortranParser
   omp_gen
   acc_gen
 )
+
+target_precompile_headers(FortranParser PRIVATE
+  [["flang/Parser/parsing.h"]]
+  [["flang/Parser/parse-tree.h"]]
+  [["flang/Parser/provenance.h"]]
+  [["flang/Parser/message.h"]]
+  [["flang/Parser/parse-tree-visitor.h"]]
+)

flang/lib/Semantics/CMakeLists.txt

@@ -64,3 +64,12 @@ add_flang_library(FortranSemantics
   FrontendOpenACC
   TargetParser
 )
+
+target_precompile_headers(FortranSemantics PRIVATE
+  [["flang/Semantics/semantics.h"]]
+  [["flang/Semantics/type.h"]]
+  [["flang/Semantics/openmp-modifiers.h"]]
+  [["flang/Semantics/expression.h"]]
+  [["flang/Semantics/tools.h"]]
+  [["flang/Semantics/symbol.h"]]
+)