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X86: Shrink certain forms of movsx.

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In particular:
movsbw %al, %ax   --> cbtw
movswl %ax, %eax  --> cwtl
movslq %eax, %rax --> cltq

According to Intel's manual those have the same performance characteristics but
come with a smaller encoding.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186174 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2013-07-12 18:06:44 +00:00
parent 2494dfcf17
commit b619dd5d5b
5 changed files with 62 additions and 6 deletions
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35
lib/Target/X86/X86MCInstLower.cpp
View File

@ -254,6 +254,34 @@ static void SimplifyShortImmForm(MCInst &Inst, unsigned Opcode) {
Inst.addOperand(Saved);
}
/// \brief If a movsx instruction has a shorter encoding for the used register
/// simplify the instruction to use it instead.
static void SimplifyMOVSX(MCInst &Inst) {
unsigned NewOpcode = 0;
unsigned Op0 = Inst.getOperand(0).getReg(), Op1 = Inst.getOperand(1).getReg();
switch (Inst.getOpcode()) {
default:
llvm_unreachable("Unexpected instruction!");
case X86::MOVSX16rr8: // movsbw %al, %ax --> cbtw
if (Op0 == X86::AX && Op1 == X86::AL)
NewOpcode = X86::CBW;
break;
case X86::MOVSX32rr16: // movswl %ax, %eax --> cwtl
if (Op0 == X86::EAX && Op1 == X86::AX)
NewOpcode = X86::CWDE;
break;
case X86::MOVSX64rr32: // movslq %eax, %rax --> cltq
if (Op0 == X86::RAX && Op1 == X86::EAX)
NewOpcode = X86::CDQE;
break;
}
if (NewOpcode != 0) {
Inst = MCInst();
Inst.setOpcode(NewOpcode);
}
}
/// \brief Simplify things like MOV32rm to MOV32o32a.
static void SimplifyShortMoveForm(X86AsmPrinter &Printer, MCInst &Inst,
unsigned Opcode) {
@ -557,6 +585,13 @@ ReSimplify:
case X86::XOR32ri: SimplifyShortImmForm(OutMI, X86::XOR32i32); break;
case X86::XOR64ri32: SimplifyShortImmForm(OutMI, X86::XOR64i32); break;
// Try to shrink some forms of movsx.
case X86::MOVSX16rr8:
case X86::MOVSX32rr16:
case X86::MOVSX64rr32:
SimplifyMOVSX(OutMI);
break;
case X86::MORESTACK_RET:
OutMI.setOpcode(X86::RET);
break;

2
test/CodeGen/X86/fast-isel-ret-ext.ll
View File

@ -26,7 +26,7 @@ define signext i16 @test4(i32 %y) nounwind {
%conv = trunc i32 %y to i16
ret i16 %conv
; CHECK: test4:
; CHECK: movswl {{.*}}, %eax
; CHECK: {{(movswl.%.x, %eax|cwtl)}}
}
define zeroext i1 @test5(i32 %y) nounwind {

18
test/CodeGen/X86/mcinst-lowering.ll
View File

@ -24,3 +24,21 @@ if.end: ; preds = %entry
return: ; preds = %entry
ret i32 0
}
define i32 @f1() nounwind {
%ax = tail call i16 asm sideeffect "", "={ax},~{dirflag},~{fpsr},~{flags}"()
%conv = sext i16 %ax to i32
ret i32 %conv
; CHECK: f1:
; CHECK: cwtl ## encoding: [0x98]
}
define i64 @f2() nounwind {
%eax = tail call i32 asm sideeffect "", "={ax},~{dirflag},~{fpsr},~{flags}"()
%conv = sext i32 %eax to i64
ret i64 %conv
; CHECK: f2:
; CHECK: cltq ## encoding: [0x48,0x98]
}

9
test/CodeGen/X86/shl_elim.ll
View File

@ -1,6 +1,4 @@
; RUN: llc < %s -march=x86 | grep "movl 8(.esp), %eax"
; RUN: llc < %s -march=x86 | grep "shrl .eax"
; RUN: llc < %s -march=x86 | grep "movswl .ax, .eax"
; RUN: llc < %s -march=x86 | FileCheck %s
define i32 @test1(i64 %a) nounwind {
%tmp29 = lshr i64 %a, 24 ; <i64> [#uses=1]
@ -9,5 +7,10 @@ define i32 @test1(i64 %a) nounwind {
%tmp45 = trunc i32 %tmp410 to i16 ; <i16> [#uses=1]
%tmp456 = sext i16 %tmp45 to i32 ; <i32> [#uses=1]
ret i32 %tmp456
; CHECK: test1:
; CHECK: movl 8(%esp), %eax
; CHECK: shrl %eax
; CHECK: cwtl
}

4
test/CodeGen/X86/widen_conv-2.ll
View File

@ -1,6 +1,6 @@
; RUN: llc < %s -march=x86 -mattr=+sse42 | FileCheck %s
; CHECK: movswl
; CHECK: movswl
; CHECK: cwtl
; CHECK: cwtl
; sign extension v2i32 to v2i16