From b70ebd2aa3b6f4546d4734e7bcdbed2017036b4d Mon Sep 17 00:00:00 2001 From: Benjamin Kramer Date: Tue, 23 Nov 2010 18:52:42 +0000 Subject: InstCombine: Reduce "X shift (A srem B)" to "X shift (A urem B)" iff B is positive. This allows to transform the rem in "1 << ((int)x % 8);" to an and. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120028 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/README.txt | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-) (limited to 'lib/Target/README.txt') diff --git a/lib/Target/README.txt b/lib/Target/README.txt index 4d5b17ab36..b98531ca85 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -1698,22 +1698,14 @@ from gcc. //===---------------------------------------------------------------------===// Missed instcombine transformation: -define i32 @a(i32 %x) nounwind readnone { -entry: - %rem = srem i32 %x, 32 - %shl = shl i32 1, %rem - ret i32 %shl -} - -The srem can be transformed to an and because if x is negative, the shift is -undefined. Here's a more general case that occurs on 64-bit targets: %382 = srem i32 %tmp14.i, 64 ; [#uses=1] %383 = zext i32 %382 to i64 ; [#uses=1] %384 = shl i64 %381, %383 ; [#uses=1] %385 = icmp slt i32 %tmp14.i, 64 ; [#uses=1] -Testcase derived from 403.gcc. +The srem can be transformed to an and because if x is negative, the shift is +undefined. Testcase derived from 403.gcc. //===---------------------------------------------------------------------===// -- cgit v1.2.3