From 48575f6ea7d5cd21ab29ca370f58fcf9ca31400b Mon Sep 17 00:00:00 2001 From: Evan Cheng Date: Sun, 5 Dec 2010 22:04:16 +0000 Subject: Making use of VFP / NEON floating point multiply-accumulate / subtraction is difficult on current ARM implementations for a few reasons. 1. Even though a single vmla has latency that is one cycle shorter than a pair of vmul + vadd, a RAW hazard during the first (4? on Cortex-a8) can cause additional pipeline stall. So it's frequently better to single codegen vmul + vadd. 2. A vmla folowed by a vmul, vmadd, or vsub causes the second fp instruction to stall for 4 cycles. We need to schedule them apart. 3. A vmla followed vmla is a special case. Obvious issuing back to back RAW vmla + vmla is very bad. But this isn't ideal either: vmul vadd vmla Instead, we want to expand the second vmla: vmla vmul vadd Even with the 4 cycle vmul stall, the second sequence is still 2 cycles faster. Up to now, isel simply avoid codegen'ing fp vmla / vmls. This works well enough but it isn't the optimial solution. This patch attempts to make it possible to use vmla / vmls in cases where it is profitable. A. Add missing isel predicates which cause vmla to be codegen'ed. B. Make sure the fmul in (fadd (fmul)) has a single use. We don't want to compute a fmul and a fmla. C. Add additional isel checks for vmla, avoid cases where vmla is feeding into fp instructions (except for the #3 exceptional case). D. Add ARM hazard recognizer to model the vmla / vmls hazards. E. Add a special pre-regalloc case to expand vmla / vmls when it's likely the vmla / vmls will trigger one of the special hazards. Work in progress, only A+B are enabled. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120960 91177308-0d34-0410-b5e6-96231b3b80d8 --- test/CodeGen/ARM/reg_sequence.ll | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'test/CodeGen/ARM/reg_sequence.ll') diff --git a/test/CodeGen/ARM/reg_sequence.ll b/test/CodeGen/ARM/reg_sequence.ll index 24eb3a8..53214fd 100644 --- a/test/CodeGen/ARM/reg_sequence.ll +++ b/test/CodeGen/ARM/reg_sequence.ll @@ -270,8 +270,9 @@ define arm_aapcs_vfpcc float @t9(%0* nocapture, %3* nocapture) nounwind { define arm_aapcs_vfpcc i32 @t10() nounwind { entry: ; CHECK: t10: +; CHECK: vmul.f32 q8, q8, d0[0] ; CHECK: vmov.i32 q9, #0x3F000000 -; CHECK: vmla.f32 q8, q8, d0[0] +; CHECK: vadd.f32 q8, q8, q8 %0 = shufflevector <4 x float> zeroinitializer, <4 x float> undef, <4 x i32> zeroinitializer ; <<4 x float>> [#uses=1] %1 = insertelement <4 x float> %0, float undef, i32 1 ; <<4 x float>> [#uses=1] %2 = insertelement <4 x float> %1, float undef, i32 2 ; <<4 x float>> [#uses=1] -- cgit v1.1