Inspired by D133662.
Close https://github.com/llvm/llvm-project/issues/57285
When -ftime-trace is specified and the driver performs both compilation and
linking phases, the trace files are currently placed in the temporary directory
(/tmp by default on *NIX). A more sensible behavior would be to derive the trace
file names from the -o option, similar to how GCC derives auxiliary and dump
file names. Use -dumpdir (D149193) to implement the -gsplit-dwarf like behavior.
The following script demonstrates the time trace filenames.
```
#!/bin/sh -e
PATH=/tmp/Rel/bin:$PATH # adapt according to your build directory
mkdir -p d e f
echo 'int main() {}' > d/a.c
echo > d/b.c
a() { rm $1 || exit 1; }
clang -ftime-trace d/a.c d/b.c # previously /tmp/[ab]-*.json
a a-a.json; a a-b.json
clang -ftime-trace d/a.c d/b.c -o e/x # previously /tmp/[ab]-*.json
a e/x-a.json; a e/x-b.json
clang -ftime-trace d/a.c d/b.c -o e/x -dumpdir f/
a f/a.json; a f/b.json
clang -ftime-trace=f d/a.c d/b.c -o e/x
a f/a-*.json; a f/b-*.json
clang -c -ftime-trace d/a.c d/b.c
a a.json b.json
clang -c -ftime-trace=f d/a.c d/b.c
a f/a.json f/b.json
clang -c -ftime-trace d/a.c -o e/xa.o
a e/xa.json
clang -c -ftime-trace d/a.c -o e/xa.o -dumpdir f/g
a f/ga.json
```
The driver checks `-ftime-trace` and `-ftime-trace=`, infers the trace file
name, and passes `-ftime-trace=` to cc1. The `-ftime-trace` cc1 option is
removed.
With offloading, previously `-ftime-trace` is passed to all offloading
actions, causing the same trace file to be overwritten by host and
offloading actions. This patch doesn't attempt to support offloading (D133662),
but makes a sensible change (`OffloadingPrefix.empty()`) to ensure we don't
overwrite the trace file.
Minor behavior differences: the trace file is now a result file, which
will be removed upon an error. -ftime-trace-granularity=0, like
-ftime-trace, can now cause a -Wunused-command-line-argument warning.
Reviewed By: Maetveis
Differential Revision: https://reviews.llvm.org/D150282
49b87b0572