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llvm-mirror/test/CodeGen/X86/sdiv-exact.ll
Benjamin Kramer 44c76d239a Emit a more efficient magic number multiplication for exact sdivs.
We have to do this in DAGBuilder instead of DAGCombiner, because the exact bit is lost after building.

  struct foo { char x[24]; };
  long bar(struct foo *a, struct foo *b) { return a-b; }
is now compiled into
  movl	4(%esp), %eax
  subl	8(%esp), %eax
  sarl	$3, %eax
  imull	$-1431655765, %eax, %eax
instead of
  movl	4(%esp), %eax
  subl	8(%esp), %eax
  movl	$715827883, %ecx
  imull	%ecx
  movl	%edx, %eax
  shrl	$31, %eax
  sarl	$2, %edx
  addl	%eax, %edx
  movl	%edx, %eax

llvm-svn: 134695
2011-07-08 10:31:30 +00:00

19 lines
351 B
LLVM

; RUN: llc -march=x86 < %s | FileCheck %s
define i32 @test1(i32 %x) {
%div = sdiv exact i32 %x, 25
ret i32 %div
; CHECK: test1:
; CHECK: imull $-1030792151, 4(%esp)
; CHECK-NEXT: ret
}
define i32 @test2(i32 %x) {
%div = sdiv exact i32 %x, 24
ret i32 %div
; CHECK: test2:
; CHECK: sarl $3
; CHECK-NEXT: imull $-1431655765
; CHECK-NEXT: ret
}