Teach 2addr pass to be do more commuting. If both uses of a two-address instruction are killed, but the first operand has a use before and after the def, commute if the second operand does not suffer from the same issue.
%reg1028<def> = EXTRACT_SUBREG %reg1027<kill>, 1
%reg1029<def> = MOV8rr %reg1028
%reg1029<def> = SHR8ri %reg1029, 7, %EFLAGS<imp-def,dead>
insert => %reg1030<def> = MOV8rr %reg1028
%reg1030<def> = ADD8rr %reg1028<kill>, %reg1029<kill>, %EFLAGS<imp-def,dead>
In this case, it might not be possible to coalesce the second MOV8rr
instruction if the first one is coalesced. So it would be profitable to
commute it:
%reg1028<def> = EXTRACT_SUBREG %reg1027<kill>, 1
%reg1029<def> = MOV8rr %reg1028
%reg1029<def> = SHR8ri %reg1029, 7, %EFLAGS<imp-def,dead>
insert => %reg1030<def> = MOV8rr %reg1029
%reg1030<def> = ADD8rr %reg1029<kill>, %reg1028<kill>, %EFLAGS<imp-def,dead>
llvm-svn: 62954
diff --git a/llvm/test/CodeGen/X86/twoaddr-coalesce.ll b/llvm/test/CodeGen/X86/twoaddr-coalesce.ll
new file mode 100644
index 0000000..c369d91
--- /dev/null
+++ b/llvm/test/CodeGen/X86/twoaddr-coalesce.ll
@@ -0,0 +1,25 @@
+; RUN: llvm-as < %s | llc -march=x86 -join-cross-class-copies -stats |& \
+; RUN: grep {twoaddrinstr} | grep {Number of instructions aggressively commuted}
+; rdar://6523745
+
+@"\01LC" = internal constant [4 x i8] c"%d\0A\00" ; <[4 x i8]*> [#uses=1]
+
+define i32 @main() nounwind {
+bb1.thread:
+ br label %bb1
+
+bb1: ; preds = %bb1, %bb1.thread
+ %i.0.reg2mem.0 = phi i32 [ 0, %bb1.thread ], [ %indvar.next, %bb1 ] ; <i32> [#uses=2]
+ %0 = trunc i32 %i.0.reg2mem.0 to i8 ; <i8> [#uses=1]
+ %1 = sdiv i8 %0, 2 ; <i8> [#uses=1]
+ %2 = sext i8 %1 to i32 ; <i32> [#uses=1]
+ %3 = tail call i32 (i8*, ...)* @printf(i8* getelementptr ([4 x i8]* @"\01LC", i32 0, i32 0), i32 %2) nounwind ; <i32> [#uses=0]
+ %indvar.next = add i32 %i.0.reg2mem.0, 1 ; <i32> [#uses=2]
+ %exitcond = icmp eq i32 %indvar.next, 258 ; <i1> [#uses=1]
+ br i1 %exitcond, label %bb2, label %bb1
+
+bb2: ; preds = %bb1
+ ret i32 0
+}
+
+declare i32 @printf(i8*, ...) nounwind