On Wed, May 18, 2022 at 6:55 PM Roger Sayle <ro...@nextmovesoftware.com> wrote: > > > The patch is a revised solution for PR middle-end/98865 incorporating > the feedback/suggestions from Richard Biener's review here: > https://gcc.gnu.org/pipermail/gcc-patches/2022-May/593928.html > Most significantly, this patch now performs the transformation/optimization > during RTL expansion, where the target's rtx_costs can be used to determine > whether the original multiplication (that may be possibly be implemented by > a shift or lea) is cheaper than a negation and a bit-wise and. > > Previously the expression (x>>63)*y would be compiled with -O2 as > shrq $63, %rdi > movq %rdi, %rax > imulq %rsi, %rax > > but with this patch now produces: > sarq $63, %rdi > movq %rdi, %rax > andq %rsi, %rax > > Likewise the expression (x>>63)*135 [that appears in a hot-spot of the > Botan AES-128 benchmark] was previously: > > shrq $63, %rdi > leaq (%rdi,%rdi,8), %rdx > movq %rdx, %rax > salq $4, %rax > subq %rdx, %rax > > now becomes: > movq %rdi, %rax > sarq $63, %rax > andl $135, %eax > > > This patch has been tested on x86_64-pc-linux-gnu with make bootstrap and > make -k check, both with and without --target_board=unix{-m32}, with no > new failures. Many thanks to Uros for the speedy review and approval of > my x86_rtx_costs patch that enables this transformation on -m32 using the > correct cost of DImode multiplication. Ok for mainline?
Looks good to me Thanks, Richard. > 2022-05-18 Roger Sayle <ro...@nextmovesoftware.com> > > gcc/ChangeLog > PR middle-end/98865 > * expr.cc (expand_expr_real_2) [MULT_EXPR]: Expand X*Y as X&Y > when both X and Y are [0, 1], X*Y as X&-Y when Y is [0,1] and > likewise X*Y as -X&Y when X is [0,1] using tree_nonzero_bits. > > gcc/testsuite/ChangeLog > PR middle-end/98865 > * gcc.target/i386/pr98865.c: New test case. > > > Thanks in advance, > Roger > -- >
