feat(build): enable link-time optimization by default

Enable LTO by default for all platforms and compilers. LTO performs
optimisation at link-time rather than at compilation time, and allows
optimisations to be made across compilation unit boundaries (i.e. C
files). This is especially useful in areas with lots of closely related
compilation units that operate on the same data structures (eg PSCI and
context management).

The only drawback is that LTO makes conditions ripe for the build to
heavily mangle all functions, making debugging a nightmare. So only
enable for release builds.

Note this will make object files unintepretable by objdump. Use lto-dump
instead.

BREAKING-CHANGE: LTO has been enabled by default, which may cause
 unpredictable issues for platforms where the linker scripts have not
 been designed with LTO in mind. Please report any issues to the
 [mailing list](mailto:tf-a@lists.trustedfirmware.org).

Change-Id: Ia472aff1a23366d918abded7a1c5da695f2c4787
Co-authored-by: Chris Kay <chris.kay@arm.com>
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index c96fcd2fc..c7a39ac65 100644
--- a/Makefile
+++ b/Makefile
@@ -141,6 +141,12 @@ else
 	BUILD_TYPE	:=	release
 	# Use LOG_LEVEL_NOTICE by default for release builds
 	LOG_LEVEL	:=	20
+        # Enable link-time optimization (AKA "inter-procedural optimization")
+        ifeq (${ARCH},aarch64)
+                ifeq ($($(ARCH)-ld-id),$($(ARCH)-cc-id))
+                        ENABLE_LTO :=	1
+                endif
+        endif
 endif #(Debug)
 
 # Default build string (git branch and commit)