On Sun, Aug 8, 2021 at 12:43 PM Roger Sayle <ro...@nextmovesoftware.com> wrote: > > > This middle-end patch implements several related improvements to > tree-ssa's conditional (bit) constant propagation pass. The current > code handling ordered comparisons contains the comment "If the > most significant bits are not known we know nothing" which is not > entirely true [this test even prevents this pass understanding these > comparisons always have a zero or one result]. This patch introduces > a new value_mask_to_min_max helper function, that understands the > different semantics of the most significant bit on signed vs. > unsigned values. This allows us to generalize ordered comparisons, > GE_EXPR, GT_EXPR, LE_EXPR and LT_EXPR, where the code is tweaked to > correctly handle the potential equal cases. Then finally support > is added for the related tree codes MIN_EXPR, MAX_EXPR, ABS_EXPR > and ABSU_EXPR. > > Regression testing revealed three test cases in the testsuite that > were checking for specific optimizations that are now being performed > earlier than expected. These tests can continue to check their > original transformations by explicitly adding -fno-tree-ccp to their > dg-options (some already specify -fno-ipa-vrp or -fno-tree-forwprop > for the same reason). > > This patch has been tested on x86_64-pc-linux-gnu with a > "make bootstrap" and "make -k check" with no new failures. > > Ok for mainline?
OK. Thanks, Richard. > > 2021-08-08 Roger Sayle <ro...@nextmovesoftware.com> > > gcc/ChangeLog > * tree-ssa-ccp.c (value_mask_to_min_max): Helper function to > determine the upper and lower bounds from a mask-value pair. > (bit_value_unop) [ABS_EXPR, ABSU_EXPR]: Add support for > absolute value and unsigned absolute value expressions. > (bit_value_binop): Initialize *VAL's precision. > [LT_EXPR, LE_EXPR]: Use value_mask_to_min_max to determine > upper and lower bounds of operands. Add LE_EXPR/GE_EXPR > support when the operands are unknown but potentially equal. > [MIN_EXPR, MAX_EXPR]: Support minimum/maximum expressions. > > gcc/testsuite/ChangeLog > * gcc.dg/pr68217.c: Add -fno-tree-ccp option. > * gcc.dg/tree-ssa/vrp24.c: Add -fno-tree-ccp option. > * g++.dg/ipa/pure-const-3.C: Add -fno-tree-ccp option. > > Roger > -- > Roger Sayle > NextMove Software > Cambridge, UK >
