[SelectionDAG] Codesize: don't expand SHIFT to SHIFT_PARTS

And instead just generate a libcall. My motivating example on ARM was a simple:
  
  shl i64 %A, %B

for which the code bloat is quite significant. For other targets that also
accept __int128/i128 such as AArch64 and X86, it is also beneficial for these
cases to generate a libcall when optimising for minsize. On these 64-bit targets,
the 64-bits shifts are of course unaffected because the SHIFT/SHIFT_PARTS
lowering operation action is not set to custom/expand.

Differential Revision: https://reviews.llvm.org/D57386

llvm-svn: 352736

1 files changed, 32 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/ARM/shift_minsize.ll b/llvm/test/CodeGen/ARM/shift_minsize.ll
new file mode 100644
index 00000000000..4d10c64392d
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/shift_minsize.ll
@@ -0,0 +1,32 @@
+; RUN: llc -mtriple=arm-eabi %s -o - | FileCheck %s
+
+define i64 @f0(i64 %val, i64 %amt) minsize optsize {
+; CHECK-LABEL:   f0:
+; CHECK:         bl  __aeabi_llsl
+  %res = shl i64 %val, %amt
+  ret i64 %res
+}
+
+define i32 @f1(i64 %x, i64 %y) minsize optsize {
+; CHECK-LABEL:   f1:
+; CHECK:         bl  __aeabi_llsl
+	%a = shl i64 %x, %y
+	%b = trunc i64 %a to i32
+	ret i32 %b
+}
+
+define i32 @f2(i64 %x, i64 %y) minsize optsize {
+; CHECK-LABEL:   f2:
+; CHECK:         bl  __aeabi_lasr
+	%a = ashr i64 %x, %y
+	%b = trunc i64 %a to i32
+	ret i32 %b
+}
+
+define i32 @f3(i64 %x, i64 %y) minsize optsize {
+; CHECK-LABEL:   f3:
+; CHECK:         bl  __aeabi_llsr
+	%a = lshr i64 %x, %y
+	%b = trunc i64 %a to i32
+	ret i32 %b
+}