hipe_x86: LeaToAdd peephole rule

Although LEA is useful for three-address form adds, sometimes it is used
where a normal add would have sufficed (due to the addition being the
last use of one of the operands; but RTL lowering does not know that as
it does not have liveness information). As a workaround, we convert LEA
back to ADD when the destination is the same as one of the operands.

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/hipe/x86/hipe_x86_postpass.erl b/lib/hipe/x86/hipe_x86_postpass.erl
index bd232041b6..390f5bf5e7 100644
--- a/lib/hipe/x86/hipe_x86_postpass.erl
+++ b/lib/hipe/x86/hipe_x86_postpass.erl
@@ -183,6 +183,18 @@ peep([B = #alu{aluop=Op,src=#x86_imm{value=Val},dst=Dst}|Insns], Res, Lst) ->
 	    peep(Insns, [B|Res], Lst)
     end;
 
+%% LeaToAdd
+%% This rule transforms lea into add when the destination is the same as one of
+%% the operands. Sound because lea is never used where the condition codes are
+%% live (and would be clobbered by add).
+%% ----------
+peep([#lea{mem=#x86_mem{base=#x86_temp{reg=DstR},off=Src},
+	   temp=Dst=#x86_temp{reg=DstR}}|Insns], Res, Lst) ->
+     peep(Insns, [#alu{aluop='add',src=Src,dst=Dst}|Res], [leaToAdd|Lst]);
+peep([#lea{mem=#x86_mem{base=Src,off=#x86_temp{reg=DstR}},
+	   temp=Dst=#x86_temp{reg=DstR}}|Insns], Res, Lst) ->
+     peep(Insns, [#alu{aluop='add',src=Src,dst=Dst}|Res], [leaToAdd|Lst]);
+
 %% SubToDec
 %% This rule turns "subl $1,Dst; jl Lab" into "decl Dst; jl Lab", which
 %% changes reduction counter tests to use decl instead of subl.