Consider subregs when calling MI::registerDefIsDead for phys deps

The scheduling dependency graph is built bottom-up within each scheduling
region, and ScheduleDAGInstrs::addPhysRegDeps is called to add output/anti
dependencies, based on physical registers, to the SUs for instructions
based on those that come before them.

In the test case, we start before post-RA scheduling with a block that looks
like this:

...
	INLINEASM <...
andc $0,$0,$2
stdcx. $0,0,$3
bne- 1b
> [sideeffect] [mayload] [maystore] [attdialect], $0:[regdef-ec:G8RC], %X6<earlyclobber,def,dead>, $1:[mem], %X3<kill>, $2:[reguse:G8RC], %X5<kill>, $3:[reguse:G8RC], %X3, $4:[mem], %X3, $5:[clobber], %CC<earlyclobber,imp-def,dead>, <<badref>>
	...
	%X4<def,dead> = ANDIo8 %X4<kill>, 1, %CR0<imp-def,dead>, %CR0GT<imp-def>
	...
	%R29<def> = ISEL %R3<undef>, %R4<kill>, %CR0GT<kill>

where it is relevant that %CC is an alias to %CR0, and that %CR0GT is a
subregister of %CR0. However, for post-RA scheduling, no dependency was added
to prevent the INLINEASM from being scheduled in between the ANDIo8 and the
ISEL (which communicate via the %CR0GT register).

In ScheduleDAGInstrs::addPhysRegDeps, when called for the %CC operand, we'd
iterate over all of its aliases (which include %CC itself and also %CR0), and
look for previously-encountered defs of those registers. We'd find the ANDIo8,
but decide not to add a dependency between the INLINEASM and the ANDIo8 because
both the INLINEASM's def of %CC is dead, and also the ANDIo8 def of %CR0 is
dead. This ignores, however, that ANDIo8 has a non-dead def of %CR0GT, a
subregister of %CR0, and thus a dependency still must exist.

To fix this problem, when calling registerDefIsDead on the SU with the def, we
also check all subregisters for possible non-dead defs, and add the dependency
if any are found.

Fixes PR21742.

llvm-svn: 223440

2 files changed, 175 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
index d8d8422f0ed..ec376e8e7bb 100644
--- a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -310,9 +310,15 @@ void ScheduleDAGInstrs::addPhysRegDeps(SUnit *SU, unsigned OperIdx) {
       SUnit *DefSU = I->SU;
       if (DefSU == &ExitSU)
         continue;
+      auto IsDefDead = [this](SUnit *DefSU, unsigned Reg) {
+        for (MCSubRegIterator SR(Reg, TRI, true); SR.isValid(); ++SR)
+          if (!DefSU->getInstr()->registerDefIsDead(*SR))
+            return false;
+        return true;
+      };
       if (DefSU != SU &&
           (Kind != SDep::Output || !MO.isDead() ||
-           !DefSU->getInstr()->registerDefIsDead(*Alias))) {
+           !IsDefDead(DefSU, *Alias))) {
         if (Kind == SDep::Anti)
           DefSU->addPred(SDep(SU, Kind, /*Reg=*/*Alias));
         else {
diff --git a/llvm/test/CodeGen/PowerPC/subreg-postra.ll b/llvm/test/CodeGen/PowerPC/subreg-postra.ll
new file mode 100644
index 00000000000..25e23b757e7
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/subreg-postra.ll
@@ -0,0 +1,168 @@
+; RUN: llc -mcpu=pwr7 < %s | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+; Function Attrs: nounwind
+define void @jbd2_journal_commit_transaction(i32* %journal) #0 {
+entry:
+  br i1 undef, label %do.body, label %if.then5
+
+if.then5:                                         ; preds = %entry
+  unreachable
+
+do.body:                                          ; preds = %entry
+  br i1 undef, label %do.body.i, label %trace_jbd2_start_commit.exit
+
+do.body.i:                                        ; preds = %do.body
+  unreachable
+
+trace_jbd2_start_commit.exit:                     ; preds = %do.body
+  br i1 undef, label %do.body.i1116, label %trace_jbd2_commit_locking.exit
+
+do.body.i1116:                                    ; preds = %trace_jbd2_start_commit.exit
+  br i1 undef, label %if.end.i1123, label %do.body5.i1122
+
+do.body5.i1122:                                   ; preds = %do.body.i1116
+  unreachable
+
+if.end.i1123:                                     ; preds = %do.body.i1116
+  br label %trace_jbd2_commit_locking.exit
+
+trace_jbd2_commit_locking.exit:                   ; preds = %if.end.i1123, %trace_jbd2_start_commit.exit
+  br i1 undef, label %spin_unlock.exit1146, label %if.then.i.i.i.i1144
+
+if.then.i.i.i.i1144:                              ; preds = %trace_jbd2_commit_locking.exit
+  unreachable
+
+spin_unlock.exit1146:                             ; preds = %trace_jbd2_commit_locking.exit
+  br i1 undef, label %spin_unlock.exit1154, label %if.then.i.i.i.i1152
+
+if.then.i.i.i.i1152:                              ; preds = %spin_unlock.exit1146
+  br label %spin_unlock.exit1154
+
+spin_unlock.exit1154:                             ; preds = %if.then.i.i.i.i1152, %spin_unlock.exit1146
+  br i1 undef, label %do.body.i1159, label %trace_jbd2_commit_flushing.exit
+
+do.body.i1159:                                    ; preds = %spin_unlock.exit1154
+  unreachable
+
+trace_jbd2_commit_flushing.exit:                  ; preds = %spin_unlock.exit1154
+  br i1 undef, label %for.end.i, label %for.body.lr.ph.i
+
+for.body.lr.ph.i:                                 ; preds = %trace_jbd2_commit_flushing.exit
+  br i1 undef, label %spin_unlock.exit.i, label %if.then.i.i.i.i.i
+
+if.then.i.i.i.i.i:                                ; preds = %for.body.lr.ph.i
+  unreachable
+
+spin_unlock.exit.i:                               ; preds = %for.body.lr.ph.i
+  unreachable
+
+for.end.i:                                        ; preds = %trace_jbd2_commit_flushing.exit
+  br i1 undef, label %journal_submit_data_buffers.exit, label %if.then.i.i.i.i31.i
+
+if.then.i.i.i.i31.i:                              ; preds = %for.end.i
+  unreachable
+
+journal_submit_data_buffers.exit:                 ; preds = %for.end.i
+  br i1 undef, label %if.end103, label %if.then102
+
+if.then102:                                       ; preds = %journal_submit_data_buffers.exit
+  unreachable
+
+if.end103:                                        ; preds = %journal_submit_data_buffers.exit
+  br i1 undef, label %do.body.i1182, label %trace_jbd2_commit_logging.exit
+
+do.body.i1182:                                    ; preds = %if.end103
+  unreachable
+
+trace_jbd2_commit_logging.exit:                   ; preds = %if.end103
+  br i1 undef, label %for.end.i1287, label %for.body.i1277
+
+for.body.i1277:                                   ; preds = %trace_jbd2_commit_logging.exit
+  unreachable
+
+for.end.i1287:                                    ; preds = %trace_jbd2_commit_logging.exit
+  br i1 undef, label %journal_finish_inode_data_buffers.exit, label %if.then.i.i.i.i84.i
+
+if.then.i.i.i.i84.i:                              ; preds = %for.end.i1287
+  unreachable
+
+journal_finish_inode_data_buffers.exit:           ; preds = %for.end.i1287
+  br i1 undef, label %if.end256, label %if.then249
+
+if.then249:                                       ; preds = %journal_finish_inode_data_buffers.exit
+  unreachable
+
+if.end256:                                        ; preds = %journal_finish_inode_data_buffers.exit
+  br i1 undef, label %do.body277, label %if.then260
+
+if.then260:                                       ; preds = %if.end256
+  br label %do.body277
+
+do.body277:                                       ; preds = %if.then260, %if.end256
+  br label %while.body318
+
+while.body318:                                    ; preds = %wait_on_buffer.exit, %do.body277
+  %tobool.i1295 = icmp eq i64 undef, 0
+  br i1 %tobool.i1295, label %wait_on_buffer.exit, label %if.then.i1296
+
+if.then.i1296:                                    ; preds = %while.body318
+  unreachable
+
+wait_on_buffer.exit:                              ; preds = %while.body318
+  br i1 undef, label %do.body378, label %while.body318
+
+do.body378:                                       ; preds = %wait_on_buffer.exit
+  br i1 undef, label %while.end418, label %while.body392.lr.ph
+
+while.body392.lr.ph:                              ; preds = %do.body378
+  br label %while.body392
+
+while.body392:                                    ; preds = %wait_on_buffer.exit1319, %while.body392.lr.ph
+  %0 = load i8** undef, align 8
+  %add.ptr399 = getelementptr inbounds i8* %0, i64 -72
+  %b_state.i.i1314 = bitcast i8* %add.ptr399 to i64*
+  %tobool.i1316 = icmp eq i64 undef, 0
+  br i1 %tobool.i1316, label %wait_on_buffer.exit1319, label %if.then.i1317
+
+if.then.i1317:                                    ; preds = %while.body392
+  unreachable
+
+wait_on_buffer.exit1319:                          ; preds = %while.body392
+  %1 = load volatile i64* %b_state.i.i1314, align 8
+  %conv.i.i1322 = and i64 %1, 1
+  %lnot404 = icmp eq i64 %conv.i.i1322, 0
+  %.err.4 = select i1 %lnot404, i32 -5, i32 undef
+  %2 = call i64 asm sideeffect "1:.long 0x7c0000a8 $| ((($0) & 0x1f) << 21) $| (((0) & 0x1f) << 16) $| ((($3) & 0x1f) << 11) $| (((0) & 0x1) << 0) \0Aandc $0,$0,$2\0Astdcx. $0,0,$3\0Abne- 1b\0A", "=&r,=*m,r,r,*m,~{cc},~{memory}"(i64* %b_state.i.i1314, i64 262144, i64* %b_state.i.i1314, i64* %b_state.i.i1314) #1
+  %prev.i.i.i1325 = getelementptr inbounds i8* %0, i64 8
+  %3 = load i32** null, align 8
+  store i32* %3, i32** undef, align 8
+  call void @__brelse(i32* undef) #1
+  br i1 undef, label %while.end418, label %while.body392
+
+; CHECK-LABEL: @jbd2_journal_commit_transaction
+; CHECK-NOT: andi.
+; CHECK: stdcx.
+; CHECK: andi.
+; CHECK: isel
+
+while.end418:                                     ; preds = %wait_on_buffer.exit1319, %do.body378
+  %err.4.lcssa = phi i32 [ undef, %do.body378 ], [ %.err.4, %wait_on_buffer.exit1319 ]
+  br i1 undef, label %if.end421, label %if.then420
+
+if.then420:                                       ; preds = %while.end418
+  call void @jbd2_journal_abort(i32* %journal, i32 signext %err.4.lcssa) #1
+  br label %if.end421
+
+if.end421:                                        ; preds = %if.then420, %while.end418
+  unreachable
+}
+
+declare void @jbd2_journal_abort(i32*, i32 signext)
+
+declare void @__brelse(i32*)
+
+attributes #0 = { nounwind }
+attributes #1 = { nounwind }
+