[llvm] [LoongArch] Fixing the incorrect return value of LoongArchTTIImpl::getRegisterBitWidth (PR #79441)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-loongarch

Author: wanglei (wangleiat)

<details>
<summary>Changes</summary>

When we do not enable vector features, we should return the default value (`TargetTransformInfoImplBase::getRegisterBitWidth`) instead of zero.

This should fix the LoongArch buildbot breakage from #<!-- -->78943. 
https://lab.llvm.org/staging/#/builders/5

---
Full diff: https://github.com/llvm/llvm-project/pull/79441.diff


1 Files Affected:

- (modified) llvm/lib/Target/LoongArch/LoongArchTargetTransformInfo.cpp (+7-4) 


``````````diff
diff --git a/llvm/lib/Target/LoongArch/LoongArchTargetTransformInfo.cpp b/llvm/lib/Target/LoongArch/LoongArchTargetTransformInfo.cpp
index 04349aa52b54089..d47dded9ea6ecf2 100644
--- a/llvm/lib/Target/LoongArch/LoongArchTargetTransformInfo.cpp
+++ b/llvm/lib/Target/LoongArch/LoongArchTargetTransformInfo.cpp
@@ -21,17 +21,20 @@ using namespace llvm;
 
 TypeSize LoongArchTTIImpl::getRegisterBitWidth(
     TargetTransformInfo::RegisterKind K) const {
+  TypeSize DefSize = TargetTransformInfoImplBase::getRegisterBitWidth(K);
   switch (K) {
   case TargetTransformInfo::RGK_Scalar:
     return TypeSize::getFixed(ST->is64Bit() ? 64 : 32);
   case TargetTransformInfo::RGK_FixedWidthVector:
-    if (ST->hasExtLASX() && ST->hasExpAutoVec())
+    if (!ST->hasExpAutoVec())
+      return DefSize;
+    if (ST->hasExtLASX())
       return TypeSize::getFixed(256);
-    if (ST->hasExtLSX() && ST->hasExpAutoVec())
+    if (ST->hasExtLSX())
       return TypeSize::getFixed(128);
-    return TypeSize::getFixed(0);
+    [[fallthrough]];
   case TargetTransformInfo::RGK_ScalableVector:
-    return TypeSize::getScalable(0);
+    return DefSize;
   }
 
   llvm_unreachable("Unsupported register kind");

``````````

</details>


https://github.com/llvm/llvm-project/pull/79441