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[X86] 8bit divrem: Improve codegen for AH register extraction.

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For 8-bit divrems where the remainder is used, we used to generate:
    divb  %sil
    shrw  $8, %ax
    movzbl  %al, %eax

That was to avoid an H-reg access, which is problematic mainly because
it isn't possible in REX-prefixed instructions.

This patch optimizes that to:
    divb  %sil
    movzbl  %ah, %eax

To do that, we explicitly extend AH, and extract the L-subreg in the
resulting register.  The extension is done using the NOREX variants of
MOVZX.  To support signed operations, MOVSX_NOREX is also added.
Further, this introduces a new SDNode type, [us]divrem_ext_hreg, which is
then lowered to a sequence containing a single zext (rather than 2).

Differential Revision: http://reviews.llvm.org/D6064


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221176 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Ahmed Bougacha
2014-11-03 20:26:35 +00:00
parent f16d6b1ff1
commit 40453da779
5 changed files with 185 additions and 26 deletions
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100
test/CodeGen/X86/divrem8_ext.ll Normal file
View File

@@ -0,0 +1,100 @@
; RUN: llc -march=x86-64 < %s | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-64
; RUN: llc -march=x86 < %s | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-32
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.10.0"
define zeroext i8 @test_udivrem_zext_ah(i8 %x, i8 %y) {
; CHECK-LABEL: test_udivrem_zext_ah
; CHECK: divb
; CHECK: movzbl %ah, [[REG_REM:%[a-z0-9]+]]
; CHECK: movb %al, ([[REG_ZPTR:%[a-z0-9]+]])
; CHECK: movl [[REG_REM]], %eax
; CHECK: ret
%div = udiv i8 %x, %y
store i8 %div, i8* @z
%1 = urem i8 %x, %y
ret i8 %1
}
define zeroext i8 @test_urem_zext_ah(i8 %x, i8 %y) {
; CHECK-LABEL: test_urem_zext_ah
; CHECK: divb
; CHECK: movzbl %ah, %eax
; CHECK: ret
%1 = urem i8 %x, %y
ret i8 %1
}
define i8 @test_urem_noext_ah(i8 %x, i8 %y) {
; CHECK-LABEL: test_urem_noext_ah
; CHECK: divb [[REG_X:%[a-z0-9]+]]
; CHECK: movzbl %ah, %eax
; CHECK: addb [[REG_X]], %al
; CHECK: ret
%1 = urem i8 %x, %y
%2 = add i8 %1, %y
ret i8 %2
}
define i64 @test_urem_zext64_ah(i8 %x, i8 %y) {
; CHECK-LABEL: test_urem_zext64_ah
; CHECK: divb
; CHECK: movzbl %ah, %eax
; CHECK-32: xorl %edx, %edx
; CHECK: ret
%1 = urem i8 %x, %y
%2 = zext i8 %1 to i64
ret i64 %2
}
define signext i8 @test_sdivrem_sext_ah(i8 %x, i8 %y) {
; CHECK-LABEL: test_sdivrem_sext_ah
; CHECK: cbtw
; CHECK: idivb
; CHECK: movsbl %ah, [[REG_REM:%[a-z0-9]+]]
; CHECK: movb %al, ([[REG_ZPTR]])
; CHECK: movl [[REG_REM]], %eax
; CHECK: ret
%div = sdiv i8 %x, %y
store i8 %div, i8* @z
%1 = srem i8 %x, %y
ret i8 %1
}
define signext i8 @test_srem_sext_ah(i8 %x, i8 %y) {
; CHECK-LABEL: test_srem_sext_ah
; CHECK: cbtw
; CHECK: idivb
; CHECK: movsbl %ah, %eax
; CHECK: ret
%1 = srem i8 %x, %y
ret i8 %1
}
define i8 @test_srem_noext_ah(i8 %x, i8 %y) {
; CHECK-LABEL: test_srem_noext_ah
; CHECK: cbtw
; CHECK: idivb [[REG_X:%[a-z0-9]+]]
; CHECK: movsbl %ah, %eax
; CHECK: addb [[REG_X]], %al
; CHECK: ret
%1 = srem i8 %x, %y
%2 = add i8 %1, %y
ret i8 %2
}
define i64 @test_srem_sext64_ah(i8 %x, i8 %y) {
; CHECK-LABEL: test_srem_sext64_ah
; CHECK: cbtw
; CHECK: idivb
; CHECK: movsbl %ah, %eax
; CHECK-32: movl %eax, %edx
; CHECK-32: sarl $31, %edx
; CHECK-64: movsbq %al, %rax
; CHECK: ret
%1 = srem i8 %x, %y
%2 = sext i8 %1 to i64
ret i64 %2
}
@z = external global i8