llvm-6502/test/CodeGen/X86/lsr-interesting-step.ll
Tim Northover 15983b80a0 X86: use sub-register sequences for MOV*r0 operations
Instead of having a bunch of separate MOV8r0, MOV16r0, ... pseudo-instructions,
it's better to use a single MOV32r0 (which will expand to "xorl %reg, %reg")
and obtain other sizes with EXTRACT_SUBREG and SUBREG_TO_REG. The encoding is
smaller and partial register updates can sometimes be avoided.

Until recently, this sequence was a barrier to rematerialization though. That
should now be fixed so it's an appropriate time to make the change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182928 91177308-0d34-0410-b5e6-96231b3b80d8
2013-05-30 13:19:42 +00:00

52 lines
1.9 KiB
LLVM

; RUN: llc < %s -march=x86-64 -relocation-model=static -mtriple=x86_64-unknown-linux-gnu -asm-verbose=0 | FileCheck %s
; The inner loop should require only one add (and no leas either).
; rdar://8100380
; CHECK: BB0_3:
; CHECK-NEXT: movb $0, flags(%rdx)
; CHECK-NEXT: addq %rax, %rdx
; CHECK-NEXT: cmpq $8192, %rdx
; CHECK-NEXT: jl
@flags = external global [8192 x i8], align 16 ; <[8192 x i8]*> [#uses=1]
define void @foo() nounwind {
entry:
%tmp = icmp slt i64 2, 8192 ; <i1> [#uses=1]
br i1 %tmp, label %bb, label %bb21
bb: ; preds = %entry
br label %bb7
bb7: ; preds = %bb, %bb17
%tmp8 = phi i64 [ %tmp18, %bb17 ], [ 2, %bb ] ; <i64> [#uses=2]
%tmp9 = icmp slt i64 2, 8192 ; <i1> [#uses=1]
br i1 %tmp9, label %bb10, label %bb17
bb10: ; preds = %bb7
br label %bb11
bb11: ; preds = %bb10, %bb11
%tmp12 = phi i64 [ %tmp14, %bb11 ], [ 2, %bb10 ] ; <i64> [#uses=2]
%tmp13 = getelementptr inbounds [8192 x i8]* @flags, i64 0, i64 %tmp12 ; <i8*> [#uses=1]
store i8 0, i8* %tmp13, align 1
%tmp14 = add nsw i64 %tmp12, %tmp8 ; <i64> [#uses=2]
%tmp15 = icmp slt i64 %tmp14, 8192 ; <i1> [#uses=1]
br i1 %tmp15, label %bb11, label %bb16
bb16: ; preds = %bb11
br label %bb17
bb17: ; preds = %bb16, %bb7
%tmp18 = add nsw i64 %tmp8, 1 ; <i64> [#uses=2]
%tmp19 = icmp slt i64 %tmp18, 8192 ; <i1> [#uses=1]
br i1 %tmp19, label %bb7, label %bb20
bb20: ; preds = %bb17
br label %bb21
bb21: ; preds = %bb20, %entry
ret void
}