[SystemZ] Use BRCT and BRCTG to eliminate add-&-compare sequences
This patch just uses a peephole test for "add; compare; branch" sequences
within a single block. The IR optimizers already convert loops to
decrement-and-branch-on-nonzero form in some cases, so even this
simplistic test triggers many times during a clang bootstrap and
projects/test-suite run. It looks like there are still cases where we
need to more strongly prefer branches on nonzero though. E.g. I saw a
case where a loop that started out with a check for 0 ended up with a
check for -1. I'll try to look at that sometime.
I ended up adding the Reference class because MachineInstr::readsRegister()
doesn't check for subregisters (by design, as far as I could tell).
llvm-svn: 187723
diff --git a/llvm/test/CodeGen/SystemZ/Large/branch-range-08.py b/llvm/test/CodeGen/SystemZ/Large/branch-range-08.py
new file mode 100644
index 0000000..ac1b137
--- /dev/null
+++ b/llvm/test/CodeGen/SystemZ/Large/branch-range-08.py
@@ -0,0 +1,69 @@
+# Test 64-bit BRANCH RELATIVE ON COUNT in cases where some branches are out
+# of range.
+# RUN: python %s | llc -mtriple=s390x-linux-gnu | FileCheck %s
+
+# Construct:
+#
+# loopN:
+# load of countN
+# ...
+# loop0:
+# 0xffd8 bytes, from MVIY instructions
+# conditional branch to main
+# after0:
+# ...
+# decrement of countN
+# conditional branch to loopN
+# afterN:
+#
+# Each load occupies 6 bytes. Each decrement and branch occupies 4
+# bytes if BRCTG can be used, otherwise it occupies 10 bytes (AGHI + BRCL).
+# This means that loop 5 contains 4 * 6 + 0xffd8 + 4 * 4 == 0x10000 bytes
+# and is therefore (just) in range. Loop 6 is out of range.
+#
+# CHECK: brctg {{%r[0-9]+}}
+# CHECK: brctg {{%r[0-9]+}}
+# CHECK: brctg {{%r[0-9]+}}
+# CHECK: brctg {{%r[0-9]+}}
+# CHECK: brctg {{%r[0-9]+}}
+# CHECK: aghi {{%r[0-9]+}}, -1
+# CHECK: jglh
+# CHECK: aghi {{%r[0-9]+}}, -1
+# CHECK: jglh
+# CHECK: aghi {{%r[0-9]+}}, -1
+# CHECK: jglh
+
+branch_blocks = 8
+main_size = 0xffd8
+
+print 'define void @f1(i8 *%base, i64 *%counts) {'
+print 'entry:'
+
+for i in xrange(branch_blocks - 1, -1, -1):
+ print ' %%countptr%d = getelementptr i64 *%%counts, i64 %d' % (i, i)
+ print ' %%initcount%d = load i64 *%%countptr%d' % (i, i)
+ print ' br label %%loop%d' % i
+
+ print 'loop%d:' % i
+ block1 = 'entry' if i == branch_blocks - 1 else 'loop%d' % (i + 1)
+ block2 = 'loop0' if i == 0 else 'after%d' % (i - 1)
+ print (' %%count%d = phi i64 [ %%initcount%d, %%%s ],'
+ ' [ %%nextcount%d, %%%s ]' % (i, i, block1, i, block2))
+
+a, b = 1, 1
+for i in xrange(0, main_size, 6):
+ a, b = b, a + b
+ offset = 4096 + b % 500000
+ value = a % 256
+ print ' %%ptr%d = getelementptr i8 *%%base, i64 %d' % (i, offset)
+ print ' store volatile i8 %d, i8 *%%ptr%d' % (value, i)
+
+for i in xrange(branch_blocks):
+ print ' %%nextcount%d = add i64 %%count%d, -1' % (i, i)
+ print ' %%test%d = icmp ne i64 %%nextcount%d, 0' % (i, i)
+ print ' br i1 %%test%d, label %%loop%d, label %%after%d' % (i, i, i)
+ print ''
+ print 'after%d:' % i
+
+print ' ret void'
+print '}'