[llvm] [GlobalISel] Correct comment about type vs register class (PR #116083)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-globalisel

Author: Daniel Sanders (dsandersllvm)

<details>
<summary>Changes</summary>

Type and register class aren't mutually exclusive in gMIR but target
instructions don't have types on their operands that have register classes.

---
Full diff: https://github.com/llvm/llvm-project/pull/116083.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp (+10-9) 


``````````diff
diff --git a/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp b/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
index fefa8f2ea85942..179ac9deb3d4a5 100644
--- a/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
@@ -147,6 +147,16 @@ void GISelKnownBits::computeKnownBitsImpl(Register R, KnownBits &Known,
   unsigned Opcode = MI.getOpcode();
   LLT DstTy = MRI.getType(R);
 
+  // Handle the case where this is called on a register that does not have a
+  // type constraint (i.e. it's a target instruction with a register class
+  // constraint instead). This is unlikely to occur except by looking through
+  // copies but it is possible for the initial register being queried to be in
+  // this state.
+  if (!DstTy.isValid()) {
+    Known = KnownBits();
+    return;
+  }
+
 #ifndef NDEBUG
   if (DstTy.isFixedVector()) {
     assert(
@@ -158,15 +168,6 @@ void GISelKnownBits::computeKnownBitsImpl(Register R, KnownBits &Known,
   }
 #endif
 
-  // Handle the case where this is called on a register that does not have a
-  // type constraint (i.e. it has a register class constraint instead). This is
-  // unlikely to occur except by looking through copies but it is possible for
-  // the initial register being queried to be in this state.
-  if (!DstTy.isValid()) {
-    Known = KnownBits();
-    return;
-  }
-
   unsigned BitWidth = DstTy.getScalarSizeInBits();
   auto CacheEntry = ComputeKnownBitsCache.find(R);
   if (CacheEntry != ComputeKnownBitsCache.end()) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/116083