gh-160381: Show LLVM profile statistics after PGO training (#160373)

LLVM PGO builds merge the training profiles without showing the profile-count distribution or functions with the hottest basic blocks. Run `llvm-profdata show --detailed-summary --topn=500` after merging to make it easier to compare training workloads.

Addresses [astral-sh/python-build-standalone#1033](astral-sh/python-build-standalone#1033) tracking upstreaming of this patch.

Author: zanieb

Makefile.pre.in

@@ -50,6 +50,7 @@ GITBRANCH=	@GITBRANCH@
 PGO_PROF_GEN_FLAG=@PGO_PROF_GEN_FLAG@
 PGO_PROF_USE_FLAG=@PGO_PROF_USE_FLAG@
 LLVM_PROF_MERGER=@LLVM_PROF_MERGER@
+LLVM_PROF_SHOW=@LLVM_PROF_SHOW@
 LLVM_PROF_FILE=@LLVM_PROF_FILE@
 LLVM_PROF_ERR=@LLVM_PROF_ERR@
 DTRACE=         @DTRACE@
@@ -857,6 +858,7 @@ profile-run-stamp:
 	@ # FIXME: can't run for a cross build
 	$(LLVM_PROF_FILE) $(RUNSHARED) ./$(BUILDPYTHON) $(PROFILE_TASK)
 	$(LLVM_PROF_MERGER)
+	$(LLVM_PROF_SHOW)
 	# Remove profile generation binary since we are done with it.
 	$(MAKE) clean-retain-profile
 	# This is an expensive target to build and it does not have proper

configure

@@ -2292,6 +2292,7 @@ fi
 AC_SUBST([PGO_PROF_GEN_FLAG])
 AC_SUBST([PGO_PROF_USE_FLAG])
 AC_SUBST([LLVM_PROF_MERGER])
+AC_SUBST([LLVM_PROF_SHOW])
 AC_SUBST([LLVM_PROF_FILE])
 AC_SUBST([LLVM_PROF_ERR])
 AC_SUBST([LLVM_PROFDATA])
@@ -2316,6 +2317,7 @@ then
   fi
 fi
 LLVM_PROF_ERR=no
+LLVM_PROF_SHOW=true
 
 case "$ac_cv_cc_name" in
   clang|icx)
@@ -2328,6 +2330,10 @@ case "$ac_cv_cc_name" in
             \"\$(shell pwd)\"/*.profclangr
     ")
     LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"\$(shell pwd)/code-%p.profclangr\""
+    LLVM_PROF_SHOW=m4_normalize("
+        ${LLVM_PROFDATA} show --detailed-summary --topn=500
+            \"\$(shell pwd)/code.profclangd\"
+    ")
     if test $LLVM_PROF_FOUND = not-found
     then
       LLVM_PROF_ERR=yes