[NVPTX] Promote v2i8 to v2i16

[manasij7479]

Promote v2i8 to v2i16, fixes a crash.
Re-enable a test in NVPTX/vector-returns.ll

#104864

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[llvmbot]

@llvm/pr-subscribers-backend-nvptx

Author: Manasij Mukherjee (manasij7479)

Changes

Promote v2i8 to v2i16, fixes a crash.
Re-enable a test in NVPTX/vector-returns.ll

#104864

---

Full diff: https://github.com/llvm/llvm-project/pull/111189.diff

2 Files Affected:

• (modified) llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp (+4)
• (modified) llvm/test/CodeGen/NVPTX/vector-returns.ll (+11-4)

diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
index 8718b7890bf58a..57bc5fe0ac361c 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
@@ -236,6 +236,10 @@ static void ComputePTXValueVTs(const TargetLowering &TLI, const DataLayout &DL,
         // v*i8 are formally lowered as v4i8
         EltVT = MVT::v4i8;
         NumElts = (NumElts + 3) / 4;
+      } else if (EltVT.getSimpleVT() == MVT::i8 && NumElts == 2) {
+        // v2i8 is promoted to v2i16
+        NumElts = 1;
+        EltVT = MVT::v2i16;
       }
       for (unsigned j = 0; j != NumElts; ++j) {
         ValueVTs.push_back(EltVT);
diff --git a/llvm/test/CodeGen/NVPTX/vector-returns.ll b/llvm/test/CodeGen/NVPTX/vector-returns.ll
index 0d2ad2c9bee750..956f74392ae130 100644
--- a/llvm/test/CodeGen/NVPTX/vector-returns.ll
+++ b/llvm/test/CodeGen/NVPTX/vector-returns.ll
@@ -325,10 +325,17 @@ define <3 x i8> @byte3() {
   ret <3 x i8> zeroinitializer
 }
 
-; FIXME: This test causes a crash. 
-; define <2 x i8> @byte2() {
-;   ret <2 x i8> zeroinitializer
-; }
+define <2 x i8> @byte2() {
+; CHECK-LABEL: byte2(
+; CHECK:       {
+; CHECK-NEXT:    .reg .b32 %r<2>;
+; CHECK-EMPTY:
+; CHECK-NEXT:  // %bb.0:
+; CHECK-NEXT:    mov.b32 %r1, 0;
+; CHECK-NEXT:    st.param.b32 [func_retval0+0], %r1;
+; CHECK-NEXT:    ret;
+  ret <2 x i8> zeroinitializer
+}
 
 define <1 x i8> @byte1() {
 ; CHECK-LABEL: byte1(

[justinfargnoli]

Please wait for @Artem-B to review before merging.

[Artem-B]

It may be useful to use a non-zero value, so we can verify that we've stored the vector elements in correct order.
That, actually applies to all the tests here, so it may be worth fixing that in a separate patch.

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