Fix vector splitting for extract_vector_elt and vector elements of <8-bits.

Summary:
One of the vector splitting paths for extract_vector_elt tries to lower:
    define i1 @via_stack_bug(i8 signext %idx) {
      %1 = extractelement <2 x i1> <i1 false, i1 true>, i8 %idx
      ret i1 %1
    }
to:
    define i1 @via_stack_bug(i8 signext %idx) {
      %base = alloca <2 x i1>
      store <2 x i1> <i1 false, i1 true>, <2 x i1>* %base
      %2 = getelementptr <2 x i1>, <2 x i1>* %base, i32 %idx
      %3 = load i1, i1* %2
      ret i1 %3
    }
However, the elements of <2 x i1> are not byte-addressible. The result of this
is that the getelementptr expands to '%base + %idx * (1 / 8)' which simplifies
to '%base + %idx * 0', and then simply '%base' causing all values of %idx to
extract element zero.

This commit fixes this by promoting the vector elements of <8-bits to i8 before
splitting the vector.

This fixes a number of test failures in pocl.

Reviewers: pekka.jaaskelainen

Subscribers: pekka.jaaskelainen, llvm-commits

Differential Revision: http://reviews.llvm.org/D12591

llvm-svn: 247128

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/Mips/llvm-ir/extractelement.ll b/llvm/test/CodeGen/Mips/llvm-ir/extractelement.ll
new file mode 100644
index 00000000000..1e1b02df99a
--- /dev/null
+++ b/llvm/test/CodeGen/Mips/llvm-ir/extractelement.ll
@@ -0,0 +1,19 @@
+; RUN: llc < %s -march=mips -mcpu=mips2 | FileCheck %s -check-prefix=ALL
+
+; This test triggered a bug in the vector splitting where the type legalizer
+; attempted to extract the element with by storing the vector, then reading
+; an element back. However, the address calculation was:
+;   Base + Index * (EltSizeInBits / 8)
+; and EltSizeInBits was 1. This caused the index to be forgotten.
+define i1 @via_stack_bug(i8 signext %idx) {
+  %1 = extractelement <2 x i1> <i1 false, i1 true>, i8 %idx
+  ret i1 %1
+}
+
+; ALL-LABEL: via_stack_bug:
+; ALL-DAG:       addiu  [[ONE:\$[0-9]+]], $zero, 1
+; ALL-DAG:       sb     [[ONE]], 7($sp)
+; ALL-DAG:       sb     $zero, 6($sp)
+; ALL-DAG:       addiu  [[VPTR:\$[0-9]+]], $sp, 6
+; ALL-DAG:       addu   [[EPTR:\$[0-9]+]], $4, [[VPTR]]
+; ALL:           lbu    $2, 0([[EPTR]])