From 6fc631978cdd1128a790854e497e267639d9325d Mon Sep 17 00:00:00 2001 From: Derek Schuff Date: Wed, 15 May 2013 16:08:30 +0000 Subject: Support unaligned load/store on more ARM targets This patch matches GCC behavior: the code used to only allow unaligned load/store on ARM for v6+ Darwin, it will now allow unaligned load/store for v6+ Darwin as well as for v7+ on other targets. The distinction is made because v6 doesn't guarantee support (but LLVM assumes that Apple controls hardware+kernel and therefore have conformant v6 CPUs), whereas v7 does provide this guarantee (and Linux behaves sanely). Overall this should slightly improve performance in most cases because of reduced I$ pressure. Patch by JF Bastien git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181897 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/ARM/ARMSubtarget.cpp | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/lib/Target/ARM/ARMSubtarget.cpp b/lib/Target/ARM/ARMSubtarget.cpp index 8653c462f0..9ff0d61481 100644 --- a/lib/Target/ARM/ARMSubtarget.cpp +++ b/lib/Target/ARM/ARMSubtarget.cpp @@ -162,10 +162,23 @@ void ARMSubtarget::resetSubtargetFeatures(StringRef CPU, StringRef FS) { if (!isThumb() || hasThumb2()) PostRAScheduler = true; - // v6+ may or may not support unaligned mem access depending on the system - // configuration. - if (!StrictAlign && hasV6Ops() && isTargetDarwin()) - AllowsUnalignedMem = true; + if (!StrictAlign) { + // Assume pre-ARMv6 doesn't support unaligned accesses. + // + // ARMv6 may or may not support unaligned accesses depending on the + // SCTLR.U bit, which is architecture-specific. We assume ARMv6 + // Darwin targets support unaligned accesses, and others don't. + // + // ARMv7 always has SCTLR.U set to 1, but it has a new SCTLR.A bit + // which raises an alignment fault on unaligned accesses. Linux + // defaults this bit to 0 and handles it as a system-wide (not + // per-process) setting. It is therefore safe to assume that ARMv7+ + // targets support unaligned accesses. + // + // The above behavior is consistent with GCC. + if (hasV7Ops() || (hasV6Ops() && isTargetDarwin())) + AllowsUnalignedMem = true; + } // NEON f32 ops are non-IEEE 754 compliant. Darwin is ok with it by default. uint64_t Bits = getFeatureBits(); -- cgit v1.2.3