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llvm-project/llvm/test/CodeGen/X86/sdiv-exact.ll

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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 18:31:30 +08:00
; 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
}