From 713ecb3d417363a4b12c725b335fce10355da206 Mon Sep 17 00:00:00 2001 From: Jeff Law Date: Wed, 25 Mar 2020 10:37:31 -0600 Subject: [PATCH] rs6000: Allow FPRs to change between SDmode and DDmode [PR94254] g:497498c878d48754318e486428e2aa30854020b9 caused lra to cycle on some SDmode reloads for power6. As explained in more detail in the PR comments, the problem was a conflict between two target hooks: rs6000_secondary_memory_needed_mode required SDmode FPR reloads to use DDmode memory (rightly, since using SDmode memory wouldn't make progress) but rs6000_can_change_mode_class didn't allow FPRs to change from SDmode to DDmode. Previously lra ignored that and changed the mode anyway. From what Segher says, it sounds like the "from_size < 8 || to_size < 8" check is mostly there for SF<->64-bit subregs, and that SDmode is stored in the way that target-independent code expects. This patch therefore allows SD<->DD changes. I wondered about checking for SD<->64-bit changes instead, but that seemed like an unnecessary generalisation for this stage. 2020-03-23 Richard Sandiford gcc/ PR target/94254 * config/rs6000/rs6000.c (rs6000_can_change_mode_class): Allow FPRs to change between SDmode and DDmode. --- gcc/ChangeLog | 6 ++++++ gcc/config/rs6000/rs6000.c | 9 +++++++++ 2 files changed, 15 insertions(+) diff --git a/gcc/ChangeLog b/gcc/ChangeLog index b75ac74e73a..7678776c344 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,9 @@ +2020-03-25 Richard Sandiford + + PR target/94254 + * config/rs6000/rs6000.c (rs6000_can_change_mode_class): Allow + FPRs to change between SDmode and DDmode. + 2020-03-25 Martin Sebor PR tree-optimization/94131 diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c index 7505a0e1e8e..5b36593bfb7 100644 --- a/gcc/config/rs6000/rs6000.c +++ b/gcc/config/rs6000/rs6000.c @@ -12307,6 +12307,15 @@ rs6000_can_change_mode_class (machine_mode from, if (!BYTES_BIG_ENDIAN && (to == TDmode || from == TDmode)) return false; + /* Allow SD<->DD changes, since SDmode values are stored in + the low half of the DDmode, just like target-independent + code expects. We need to allow at least SD->DD since + rs6000_secondary_memory_needed_mode asks for that change + to be made for SD reloads. */ + if ((to == DDmode && from == SDmode) + || (to == SDmode && from == DDmode)) + return true; + if (from_size < 8 || to_size < 8) return false; -- 2.30.2