From 9960a25006d9907a93aae39a8bfbc478a3518a72 Mon Sep 17 00:00:00 2001 From: Benjamin Kramer Date: Fri, 8 Jul 2011 10:31:30 +0000 Subject: 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 --- llvm/test/CodeGen/X86/sdiv-exact.ll | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) create mode 100644 llvm/test/CodeGen/X86/sdiv-exact.ll (limited to 'llvm/test/CodeGen/X86/sdiv-exact.ll') diff --git a/llvm/test/CodeGen/X86/sdiv-exact.ll b/llvm/test/CodeGen/X86/sdiv-exact.ll new file mode 100644 index 00000000000..48bb8836e89 --- /dev/null +++ b/llvm/test/CodeGen/X86/sdiv-exact.ll @@ -0,0 +1,18 @@ +; 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 +} -- cgit v1.2.3