[LLVM][SVE] Ensure all fixed length mask bits are defined. (#116819)

convertFixedMaskToScalableVector expects the mask input to honour the
BoolContents scheme employed by the target. For AArch64 this means a
mask should be zero or all ones, and thus when promoting a mask we must
use a sign extend.

Author: paulwalker-arm

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -28163,7 +28163,7 @@ SDValue AArch64TargetLowering::LowerFixedLengthVectorMLoadToSVE(
   if (VT.getScalarSizeInBits() > Mask.getValueType().getScalarSizeInBits()) {
     assert(Load->getExtensionType() != ISD::NON_EXTLOAD &&
            "Incorrect mask type");
-    Mask = DAG.getNode(ISD::ANY_EXTEND, DL, VT, Mask);
+    Mask = DAG.getNode(ISD::SIGN_EXTEND, DL, VT, Mask);
   }
   Mask = convertFixedMaskToScalableVector(Mask, DAG);
 

llvm/test/CodeGen/AArch64/sve-streaming-mode-fixed-length-masked-load.ll

@@ -2677,7 +2677,7 @@ define <3 x i32> @masked_load_zext_v3i32(ptr %load_ptr, <3 x i1> %pm) {
 ; CHECK-NEXT:    and z0.d, z0.d, z1.d
 ; CHECK-NEXT:    lsl z0.h, z0.h, #15
 ; CHECK-NEXT:    asr z0.h, z0.h, #15
-; CHECK-NEXT:    uunpklo z0.s, z0.h
+; CHECK-NEXT:    sunpklo z0.s, z0.h
 ; CHECK-NEXT:    cmpne p0.s, p0/z, z0.s, #0
 ; CHECK-NEXT:    ld1h { z0.s }, p0/z, [x0]
 ; CHECK-NEXT:    // kill: def $q0 killed $q0 killed $z0
@@ -2750,7 +2750,7 @@ define <3 x i32> @masked_load_sext_v3i32(ptr %load_ptr, <3 x i1> %pm) {
 ; CHECK-NEXT:    and z0.d, z0.d, z1.d
 ; CHECK-NEXT:    lsl z0.h, z0.h, #15
 ; CHECK-NEXT:    asr z0.h, z0.h, #15
-; CHECK-NEXT:    uunpklo z0.s, z0.h
+; CHECK-NEXT:    sunpklo z0.s, z0.h
 ; CHECK-NEXT:    cmpne p0.s, p0/z, z0.s, #0
 ; CHECK-NEXT:    ld1sh { z0.s }, p0/z, [x0]
 ; CHECK-NEXT:    // kill: def $q0 killed $q0 killed $z0