Allow combining -Cprofile-generate and -Cpanic=unwind when targeting

MSVC.

The LLVM limitation that previously prevented this has been fixed in LLVM
9 which is older than the oldest LLVM version we currently support.

See rust-lang#61002.

Author: michaelwoerister

compiler/rustc_session/src/session.rs

@@ -1,7 +1,7 @@
 use crate::cgu_reuse_tracker::CguReuseTracker;
 use crate::code_stats::CodeStats;
 pub use crate::code_stats::{DataTypeKind, FieldInfo, SizeKind, VariantInfo};
-use crate::config::{self, CrateType, OutputType, PrintRequest, SwitchWithOptPath};
+use crate::config::{self, CrateType, OutputType, SwitchWithOptPath};
 use crate::filesearch;
 use crate::lint::{self, LintId};
 use crate::parse::ParseSess;
@@ -1440,25 +1440,6 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
         }
     }
 
-    // PGO does not work reliably with panic=unwind on Windows. Let's make it
-    // an error to combine the two for now. It always runs into an assertions
-    // if LLVM is built with assertions, but without assertions it sometimes
-    // does not crash and will probably generate a corrupted binary.
-    // We should only display this error if we're actually going to run PGO.
-    // If we're just supposed to print out some data, don't show the error (#61002).
-    if sess.opts.cg.profile_generate.enabled()
-        && sess.target.is_like_msvc
-        && sess.panic_strategy() == PanicStrategy::Unwind
-        && sess.opts.prints.iter().all(|&p| p == PrintRequest::NativeStaticLibs)
-    {
-        sess.err(
-            "Profile-guided optimization does not yet work in conjunction \
-                  with `-Cpanic=unwind` on Windows when targeting MSVC. \
-                  See issue #61002 <https://github.com/rust-lang/rust/issues/61002> \
-                  for more information.",
-        );
-    }
-
     // Sanitizers can only be used on platforms that we know have working sanitizer codegen.
     let supported_sanitizers = sess.target.options.supported_sanitizers;
     let unsupported_sanitizers = sess.opts.debugging_opts.sanitizer - supported_sanitizers;

src/test/codegen/pgo-instrumentation.rs

@@ -1,8 +1,7 @@
 // Test that `-Cprofile-generate` creates expected instrumentation artifacts in LLVM IR.
-// Compiling with `-Cpanic=abort` because PGO+unwinding isn't supported on all platforms.
 
 // needs-profiler-support
-// compile-flags: -Cprofile-generate -Ccodegen-units=1 -Cpanic=abort
+// compile-flags: -Cprofile-generate -Ccodegen-units=1
 
 // CHECK: @__llvm_profile_raw_version =
 // CHECK-DAG: @__profc_{{.*}}pgo_instrumentation{{.*}}some_function{{.*}} = {{.*}}global

src/test/run-make-fulldeps/pgo-branch-weights/Makefile

@@ -6,19 +6,6 @@
 
 -include ../tools.mk
 
-# This test makes sure that instrumented binaries record the right counts for
-# functions being called and branches being taken. We run an instrumented binary
-# with an argument that causes a know path through the program and then check
-# that the expected counts get added to the use-phase LLVM IR.
-
-# LLVM doesn't support instrumenting binaries that use SEH:
-# https://github.com/rust-lang/rust/issues/61002
-#
-# Things work fine with -Cpanic=abort though.
-ifdef IS_MSVC
-COMMON_FLAGS=-Cpanic=abort
-endif
-
 # For some very small programs GNU ld seems to not properly handle
 # instrumentation sections correctly. Neither Gold nor LLD have that problem.
 ifeq ($(UNAME),Linux)

src/test/run-make-fulldeps/pgo-gen-lto/Makefile

@@ -8,14 +8,6 @@
 
 COMPILE_FLAGS=-Copt-level=3 -Clto=fat -Cprofile-generate="$(TMPDIR)"
 
-# LLVM doesn't yet support instrumenting binaries that use unwinding on MSVC:
-# https://github.com/rust-lang/rust/issues/61002
-#
-# Things work fine with -Cpanic=abort though.
-ifdef IS_MSVC
-COMPILE_FLAGS+= -Cpanic=abort
-endif
-
 all:
 	$(RUSTC) $(COMPILE_FLAGS) test.rs
 	$(call RUN,test) || exit 1

src/test/run-make-fulldeps/pgo-gen-no-imp-symbols/Makefile

@@ -4,14 +4,6 @@
 
 COMPILE_FLAGS=-O -Ccodegen-units=1 -Cprofile-generate="$(TMPDIR)"
 
-# LLVM doesn't yet support instrumenting binaries that use unwinding on MSVC:
-# https://github.com/rust-lang/rust/issues/61002
-#
-# Things work fine with -Cpanic=abort though.
-ifdef IS_MSVC
-COMPILE_FLAGS+= -Cpanic=abort
-endif
-
 all:
 	$(RUSTC) $(COMPILE_FLAGS) --emit=llvm-ir test.rs
 	# We expect symbols starting with "__llvm_profile_".

src/test/run-make-fulldeps/pgo-gen/Makefile

@@ -8,14 +8,6 @@
 
 COMPILE_FLAGS=-g -Cprofile-generate="$(TMPDIR)"
 
-# LLVM doesn't yet support instrumenting binaries that use unwinding on MSVC:
-# https://github.com/rust-lang/rust/issues/61002
-#
-# Things work fine with -Cpanic=abort though.
-ifdef IS_MSVC
-COMPILE_FLAGS+= -Cpanic=abort
-endif
-
 all:
 	$(RUSTC) $(COMPILE_FLAGS) test.rs
 	$(call RUN,test) || exit 1

src/test/run-make-fulldeps/pgo-indirect-call-promotion/Makefile

@@ -6,20 +6,6 @@
 
 -include ../tools.mk
 
-# This test makes sure that indirect call promotion is performed. The test
-# programs calls the same function a thousand times through a function pointer.
-# Only PGO data provides the information that it actually always is the same
-# function. We verify that the indirect call promotion pass inserts a check
-# whether it can make a direct call instead of the indirect call.
-
-# LLVM doesn't support instrumenting binaries that use SEH:
-# https://github.com/rust-lang/rust/issues/61002
-#
-# Things work fine with -Cpanic=abort though.
-ifdef IS_MSVC
-COMMON_FLAGS=-Cpanic=abort
-endif
-
 all:
 	# We don't compile `opaque` with either optimizations or instrumentation.
 	# We don't compile `opaque` with either optimizations or instrumentation.

src/test/run-make-fulldeps/pgo-use/Makefile

@@ -18,14 +18,6 @@
 
 COMMON_FLAGS=-Copt-level=2 -Ccodegen-units=1 -Cllvm-args=-disable-preinline
 
-# LLVM doesn't support instrumenting binaries that use SEH:
-# https://github.com/rust-lang/rust/issues/61002
-#
-# Things work fine with -Cpanic=abort though.
-ifdef IS_MSVC
-COMMON_FLAGS+= -Cpanic=abort
-endif
-
 ifeq ($(UNAME),Darwin)
 # macOS does not have the `tac` command, but `tail -r` does the same thing
 TAC := tail -r