[llvm] [RISCV] Attach an implicit source operand on vector copies (PR #126155)

[Pengcheng Wang via llvm-commits]

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@@ -437,6 +437,11 @@ void RISCVInstrInfo::copyPhysRegVector(
       MIB.addReg(RISCV::VL, RegState::Implicit);
       MIB.addReg(RISCV::VTYPE, RegState::Implicit);
     }
+    // Add an implicit read of the original source to silence the verifier
+    // in the cases where some of the smaller VRs we're copying from might be
+    // undef, caused by the fact that the original, larger source VR might not
+    // be fully initialized at the time this COPY happens.
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wangpc-pp wrote:

At what time the COPY happens? Why doesn't InitUndef work at this time?

https://github.com/llvm/llvm-project/pull/126155