ARM: override cost function to re-enable ConstantHoisting (& fix it).

At some point, ARM stopped getting any benefit from ConstantHoisting because
the pass called a different variant of getIntImmCost. Reimplementing the
correct variant revealed some problems, however:

  + ConstantHoisting was modifying switch statements. This is simply invalid,
    the cases must remain integer constants no matter the notional cost.
  + ConstantHoisting was mangling alloca instructions in the entry block. These
    should be handled by FrameLowering, so constants actually have a cost of 0.
    Worse, the resulting bitcasts meant they became dynamic allocas.

rdar://25707382

llvm-svn: 266260

2 files changed, 49 insertions, 0 deletions

diff --git a/llvm/test/Transforms/ConstantHoisting/ARM/bad-cases.ll b/llvm/test/Transforms/ConstantHoisting/ARM/bad-cases.ll
new file mode 100644
index 00000000000..3602eb9f3fd
--- /dev/null
+++ b/llvm/test/Transforms/ConstantHoisting/ARM/bad-cases.ll
@@ -0,0 +1,47 @@
+; RUN: opt -consthoist -S < %s | FileCheck %s
+target triple = "thumbv6m-none-eabi"
+
+; Allocas in the entry block get handled (for free) by
+; prologue/epilogue. Elsewhere they're fair game though.
+define void @avoid_allocas() {
+; CHECK-LABEL: @avoid_allocas
+; CHECK: %addr1 = alloca i8, i32 1000
+; CHECK: %addr2 = alloca i8, i32 1020
+
+  %addr1 = alloca i8, i32 1000
+  %addr2 = alloca i8, i32 1020
+  br label %elsewhere
+
+elsewhere:
+; CHECK: [[BASE:%.*]] = bitcast i32 1000 to i32
+; CHECK: alloca i8, i32 [[BASE]]
+; CHECK: [[NEXT:%.*]] = add i32 [[BASE]], 20
+; CHECK: alloca i8, i32 [[NEXT]]
+
+  %addr3 = alloca i8, i32 1000
+  %addr4 = alloca i8, i32 1020
+
+  ret void
+}
+
+; The case values of switch instructions are required to be constants.
+define void @avoid_switch(i32 %in) {
+; CHECK-LABEL: @avoid_switch
+; CHECK:   switch i32 %in, label %default [
+; CHECK:       i32 1000, label %bb1
+; CHECK:       i32 1020, label %bb2
+; CHECK:   ]
+
+  switch i32 %in, label %default
+      [ i32 1000, label %bb1
+        i32 1020, label %bb2 ]
+
+bb1:
+  ret void
+
+bb2:
+  ret void
+
+default:
+  ret void
+}
diff --git a/llvm/test/Transforms/ConstantHoisting/ARM/lit.local.cfg b/llvm/test/Transforms/ConstantHoisting/ARM/lit.local.cfg
new file mode 100644
index 00000000000..236e1d34416
--- /dev/null
+++ b/llvm/test/Transforms/ConstantHoisting/ARM/lit.local.cfg
@@ -0,0 +1,2 @@
+if not 'ARM' in config.root.targets:
+    config.unsupported = True