diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 910eb398c9f41f231135b212b165e33712d91474..1e0a0f48f74ca59a7c46255ec8129bbe2b8091cc 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,9 @@ +2005-03-14 Alexandre Oliva <aoliva@redhat.com> + + PR middle-end/18628 + * cse.c (fold_rtx_mem): Don't fold a load from a jumptable into a + register. + 2005-03-14 Alexandre Oliva <aoliva@redhat.com> PR c++/20280 diff --git a/gcc/cse.c b/gcc/cse.c index d7f3027e2bb48129eb776669609d7cef31fdbd8c..fd5e21ac2ee13f3b9a2a9fe78afb64e5303c46c2 100644 --- a/gcc/cse.c +++ b/gcc/cse.c @@ -3515,8 +3515,30 @@ fold_rtx_mem (rtx x, rtx insn) if (offset >= 0 && (offset / GET_MODE_SIZE (GET_MODE (table)) < XVECLEN (table, 0))) - return XVECEXP (table, 0, - offset / GET_MODE_SIZE (GET_MODE (table))); + { + rtx label = XVECEXP + (table, 0, offset / GET_MODE_SIZE (GET_MODE (table))); + rtx set; + + /* If we have an insn that loads the label from the + jumptable into a reg, we don't want to set the reg + to the label, because this may cause a reference to + the label to remain after the label is removed in + some very obscure cases (PR middle-end/18628). */ + if (!insn) + return label; + + set = single_set (insn); + + if (! set || SET_SRC (set) != x) + return x; + + /* If it's a jump, it's safe to reference the label. */ + if (SET_DEST (set) == pc_rtx) + return label; + + return x; + } } if (table_insn && JUMP_P (table_insn) && GET_CODE (PATTERN (table_insn)) == ADDR_DIFF_VEC) diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 4e18492dbab3af61415066e5dc928187608f2e7c..3053e823e8f68ec112ecb2667e400ca7b05b2ae5 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,7 @@ +2005-03-14 Alexandre Oliva <aoliva@redhat.com> + + * gcc.dg/pr18628.c: New. + 2005-03-14 Alexandre Oliva <aoliva@redhat.com> PR c++/20280 diff --git a/gcc/testsuite/gcc.dg/pr18628.c b/gcc/testsuite/gcc.dg/pr18628.c new file mode 100644 index 0000000000000000000000000000000000000000..d365075b7291a3bac626879892f15b4d17eebe3d --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr18628.c @@ -0,0 +1,31 @@ +/* { dg-do link } */ +/* { dg-options "-O2" } */ + +/* PR middle-end/18628 exposed a problem in which cse folded a load + from a jump table into the label that was the target of the branch. + Unfortunately, the indirect jump was moved to a different basic + block, and the LABEL_REF copied to the register wasn't enough to + keep the cfg from optimizing the otherwise-unused label away. So + we ended up with a dangling reference to the label. */ + +int i; + +int main() +{ + for (;;) + { + switch (i) + { + case 0: + case 1: + return 1; + + case 2: + case 3: + return 0; + + case 5: + --i; + } + } +}