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| author | Benjamin Kramer <benny.kra@googlemail.com> | 2011-07-08 10:31:30 +0000 |
|---|---|---|
| committer | Benjamin Kramer <benny.kra@googlemail.com> | 2011-07-08 10:31:30 +0000 |
| commit | 9c64030445cbe6ac486b90c5f459f91e06770474 (patch) | |
| tree | 54fd00aa621f35212da8d6fd83e840288382771f /test | |
| parent | ebdeeab812beec0385b445f3d4c41a114e0d972f (diff) | |
| download | llvm-9c64030445cbe6ac486b90c5f459f91e06770474.tar.gz llvm-9c64030445cbe6ac486b90c5f459f91e06770474.tar.bz2 llvm-9c64030445cbe6ac486b90c5f459f91e06770474.tar.xz | |
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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134695 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'test')
| -rw-r--r-- | test/CodeGen/X86/sdiv-exact.ll | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/test/CodeGen/X86/sdiv-exact.ll b/test/CodeGen/X86/sdiv-exact.ll new file mode 100644 index 0000000000..48bb8836e8 --- /dev/null +++ b/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 +} |