[HEXAGON] [MachinePipeliner] Fix the DAG in case of dependent phis.

%3:intregs = PHI %21:intregs, %bb.6, %7:intregs, %bb.1 - SU0
%7:intregs = PHI %21:intregs, %bb.6, %13:intregs, %bb.1 - SU1
%27:intregs = A2_zxtb %3:intregs - SU2
%13:intregs = C2_muxri %45:predregs, 0, %46:intreg

If we have dependent phis, SU0 should be the successor of SU1 not
the other way around.

Author: quic-asaravan

llvm/test/CodeGen/Hexagon/swp-dep-phis.ll

@@ -0,0 +1,96 @@
+;RUN: llc -march=hexagon -mv71t -O2 < %s -o - 2>&1 > /dev/null
+
+; Validate that we do not crash while running this test.
+;%3:intregs = PHI %21:intregs, %bb.6, %7:intregs, %bb.1 - SU0
+;%7:intregs = PHI %21:intregs, %bb.6, %13:intregs, %bb.1 - SU1
+;%27:intregs = A2_zxtb %3:intregs - SU2
+;%13:intregs = C2_muxri %45:predregs, 0, %46:intreg
+;If we have dependent phis, SU0 should be the successor of SU1 not
+;the other way around. (it used to be SU1 is the successor of SU0).
+;In some cases, SU0 is scheduled earlier than SU1 resulting in bad
+;IR as we do not have a value that can be used by SU2.
+
+@global = common dso_local local_unnamed_addr global ptr null, align 4
+@global.1 = common dso_local local_unnamed_addr global i32 0, align 4
+@global.2 = common dso_local local_unnamed_addr global i16 0, align 2
+@global.3 = common dso_local local_unnamed_addr global i16 0, align 2
+@global.4 = common dso_local local_unnamed_addr global i32 0, align 4
+
+; Function Attrs: nofree norecurse nosync nounwind
+define dso_local i32 @wombat(i8 zeroext %arg) local_unnamed_addr #0 {
+bb:
+  %load = load ptr, ptr @global, align 4
+  %load1 = load i32, ptr @global.1, align 4
+  %add2 = add nsw i32 %load1, -1
+  store i32 %add2, ptr @global.1, align 4
+  %icmp = icmp eq i32 %load1, 0
+  br i1 %icmp, label %bb36, label %bb3
+
+bb3:                                              ; preds = %bb3, %bb
+  %phi = phi i32 [ %add30, %bb3 ], [ %add2, %bb ]
+  %phi4 = phi i8 [ %phi8, %bb3 ], [ %arg, %bb ]
+  %phi5 = phi i16 [ %select23, %bb3 ], [ undef, %bb ]
+  %phi6 = phi i16 [ %select26, %bb3 ], [ undef, %bb ]
+  %phi7 = phi i16 [ %select, %bb3 ], [ undef, %bb ]
+  %phi8 = phi i8 [ %select29, %bb3 ], [ %arg, %bb ]
+  %zext = zext i8 %phi4 to i32
+  %getelementptr = getelementptr inbounds i32, ptr %load, i32 %zext
+  %getelementptr9 = getelementptr inbounds i32, ptr %getelementptr, i32 2
+  %ptrtoint = ptrtoint ptr %getelementptr9 to i32
+  %trunc = trunc i32 %ptrtoint to i16
+  %sext10 = sext i16 %phi7 to i32
+  %shl11 = shl i32 %ptrtoint, 16
+  %ashr = ashr exact i32 %shl11, 16
+  %icmp12 = icmp slt i32 %ashr, %sext10
+  %select = select i1 %icmp12, i16 %trunc, i16 %phi7
+  %getelementptr13 = getelementptr inbounds i32, ptr %getelementptr, i32 3
+  %load14 = load i32, ptr %getelementptr13, align 4
+  %shl = shl i32 %load14, 8
+  %getelementptr15 = getelementptr inbounds i32, ptr %getelementptr, i32 1
+  %load16 = load i32, ptr %getelementptr15, align 4
+  %shl17 = shl i32 %load16, 16
+  %ashr18 = ashr exact i32 %shl17, 16
+  %add = add nsw i32 %ashr18, %load14
+  %lshr = lshr i32 %add, 8
+  %or = or i32 %lshr, %shl
+  %sub = sub i32 %or, %load16
+  %trunc19 = trunc i32 %sub to i16
+  %sext = sext i16 %phi5 to i32
+  %shl20 = shl i32 %sub, 16
+  %ashr21 = ashr exact i32 %shl20, 16
+  %icmp22 = icmp sgt i32 %ashr21, %sext
+  %select23 = select i1 %icmp22, i16 %trunc19, i16 %phi5
+  %sext24 = sext i16 %phi6 to i32
+  %icmp25 = icmp slt i32 %ashr21, %sext24
+  %select26 = select i1 %icmp25, i16 %trunc19, i16 %phi6
+  %icmp27 = icmp eq i8 %phi8, 0
+  %add28 = add i8 %phi8, -1
+  %select29 = select i1 %icmp27, i8 0, i8 %add28
+  %add30 = add nsw i32 %phi, -1
+  %icmp31 = icmp eq i32 %phi, 0
+  br i1 %icmp31, label %bb32, label %bb3
+
+bb32:                                             ; preds = %bb3
+  store i16 %trunc, ptr @global.2, align 2
+  store i16 %trunc19, ptr @global.3, align 2
+  store i32 -1, ptr @global.1, align 4
+  %sext33 = sext i16 %select to i32
+  %sext34 = sext i16 %select23 to i32
+  %sext35 = sext i16 %select26 to i32
+  br label %bb36
+
+bb36:                                             ; preds = %bb32, %bb
+  %phi37 = phi i32 [ %sext33, %bb32 ], [ 0, %bb ]
+  %phi38 = phi i32 [ %sext35, %bb32 ], [ 0, %bb ]
+  %phi39 = phi i32 [ %sext34, %bb32 ], [ 0, %bb ]
+  %sub40 = sub nsw i32 %phi39, %phi38
+  %icmp41 = icmp slt i32 %sub40, %phi37
+  br i1 %icmp41, label %bb43, label %bb42
+
+bb42:                                             ; preds = %bb36
+  store i32 0, ptr @global.4, align 4
+  br label %bb43
+
+bb43:                                             ; preds = %bb42, %bb36
+  ret i32 undef
+}