[DAGCombiner] fold binops with constant into select-of-constants

This is part of the ongoing attempt to improve select codegen for all targets and select 
canonicalization in IR (see D24480 for more background). The transform is a subset of what
is done in InstCombine's FoldOpIntoSelect().

I first noticed a regression in the x86 avx512-insert-extract.ll tests with a patch that 
hopes to convert more selects to basic math ops. This appears to be a general missing DAG
transform though, so I added tests for all standard binops in rL296621 
(PowerPC was chosen semi-randomly; it has scripted FileCheck support, but so do ARM and x86).

The poor output for "sel_constants_shl_constant" is tracked with:
https://bugs.llvm.org/show_bug.cgi?id=32105

Differential Revision: https://reviews.llvm.org/D30502

llvm-svn: 296699

1 files changed, 5 insertions, 7 deletions

diff --git a/llvm/test/CodeGen/ARM/select_xform.ll b/llvm/test/CodeGen/ARM/select_xform.ll
index 8c1502e1465..09e8ed4bc09 100644
--- a/llvm/test/CodeGen/ARM/select_xform.ll
+++ b/llvm/test/CodeGen/ARM/select_xform.ll
@@ -223,21 +223,19 @@ entry:
   ret i32 %add
 }
 
-; Do not fold the xor into the select
+; Fold the xor into the select.
 define i32 @t15(i32 %p) {
 entry:
 ; ARM-LABEL: t15:
-; ARM: mov     [[REG:r[0-9]+]], #2
+; ARM: mov     [[REG:r[0-9]+]], #3
 ; ARM: cmp     r0, #8
-; ARM: movwgt  [[REG:r[0-9]+]], #1
-; ARM: eor     r0, [[REG:r[0-9]+]], #1
+; ARM: movwgt  [[REG:r[0-9]+]], #0
 
 ; T2-LABEL: t15:
-; T2: movs    [[REG:r[0-9]+]], #2
+; T2: movs    [[REG:r[0-9]+]], #3
 ; T2: cmp     [[REG:r[0-9]+]], #8
 ; T2: it      gt
-; T2: movgt   [[REG:r[0-9]+]], #1
-; T2: eor     r0, [[REG:r[0-9]+]], #1
+; T2: movgt   [[REG:r[0-9]+]], #0
   %cmp = icmp sgt i32 %p, 8
   %a = select i1 %cmp, i32 1, i32 2
   %xor = xor i32 %a, 1