Emit error when trying to use PGO in conjunction with unwinding on Windows.

src/librustc/session/mod.rs

@@ -1281,6 +1281,18 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
                               path.display()));
         }
     }
+
+    // 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.
+    if sess.opts.debugging_opts.pgo_gen.enabled() &&
+       sess.target.target.options.is_like_msvc &&
+       sess.panic_strategy() == PanicStrategy::Unwind {
+        sess.err("Profile-guided optimization does not yet work in conjunction \
+                  with `-Cpanic=unwind` on Windows when targeting MSVC. \
+                  See https://github.com/rust-lang/rust/issues/61002 for details.");
+    }
 }
 
 /// Hash value constructed out of all the `-C metadata` arguments passed to the

src/test/codegen/pgo-instrumentation.rs

@@ -1,20 +1,23 @@
 // Test that `-Zpgo-gen` 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: -Z pgo-gen -Ccodegen-units=1
+// compile-flags: -Z pgo-gen -Ccodegen-units=1 -Cpanic=abort
 
 // CHECK: @__llvm_profile_raw_version =
 // CHECK: @__profc_{{.*}}pgo_instrumentation{{.*}}some_function{{.*}} = private global
 // CHECK: @__profd_{{.*}}pgo_instrumentation{{.*}}some_function{{.*}} = private global
-// CHECK: @__profc_{{.*}}pgo_instrumentation{{.*}}main{{.*}} = private global
-// CHECK: @__profd_{{.*}}pgo_instrumentation{{.*}}main{{.*}} = private global
+// CHECK: @__profc_{{.*}}pgo_instrumentation{{.*}}some_other_function{{.*}} = private global
+// CHECK: @__profd_{{.*}}pgo_instrumentation{{.*}}some_other_function{{.*}} = private global
 // CHECK: @__llvm_profile_filename = {{.*}}"default_%m.profraw\00"{{.*}}
 
+#![crate_type="lib"]
+
 #[inline(never)]
 fn some_function() {
 
 }
 
-fn main() {
+pub fn some_other_function() {
     some_function();
 }

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

@@ -2,7 +2,17 @@
 
 -include ../tools.mk
 
+COMPILE_FLAGS=-Copt-level=3 -Clto=fat -Z pgo-gen="$(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:
-	$(RUSTC) -Copt-level=3 -Clto=fat -Z pgo-gen="$(TMPDIR)" test.rs
+	$(RUSTC) $(COMPILE_FLAGS) test.rs
 	$(call RUN,test) || exit 1
 	[ -e "$(TMPDIR)"/default_*.profraw ] || (echo "No .profraw file"; exit 1)

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

@@ -2,8 +2,18 @@
 
 -include ../tools.mk
 
+COMPILE_FLAGS=-O -Ccodegen-units=1 -Z pgo-gen="$(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:
-	$(RUSTC) -O -Ccodegen-units=1 -Z pgo-gen="$(TMPDIR)" --emit=llvm-ir test.rs
+	$(RUSTC) $(COMPILE_FLAGS) --emit=llvm-ir test.rs
 	# We expect symbols starting with "__llvm_profile_".
 	$(CGREP) "__llvm_profile_" < $(TMPDIR)/test.ll
 	# We do NOT expect the "__imp_" version of these symbols.

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

@@ -2,7 +2,17 @@
 
 -include ../tools.mk
 
+COMPILE_FLAGS=-g -Z pgo-gen="$(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:
-	$(RUSTC) -g -Z pgo-gen="$(TMPDIR)" test.rs
+	$(RUSTC) $(COMPILE_FLAGS) test.rs
 	$(call RUN,test) || exit 1
 	[ -e "$(TMPDIR)"/default_*.profraw ] || (echo "No .profraw file"; exit 1)

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

@@ -16,7 +16,7 @@
 COMMON_FLAGS=-Copt-level=s -Ccodegen-units=1
 
 # LLVM doesn't support instrumenting binaries that use SEH:
-# https://bugs.llvm.org/show_bug.cgi?id=41279
+# https://github.com/rust-lang/rust/issues/61002
 #
 # Things work fine with -Cpanic=abort though.
 ifdef IS_MSVC