[llvm] [AMDGPU] Disallow negative s_load offsets in isLegalAddressingMode (PR #91327)

[Jay Foad via llvm-commits]

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@@ -1604,6 +1604,14 @@ bool SITargetLowering::isLegalAddressingMode(const DataLayout &DL,
         return false;
     }
 
+    if (AS == AMDGPUAS::CONSTANT_ADDRESS && AM.BaseOffs < 0) {
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jayfoad wrote:

I specifically didn't want to include constant_32bit because I saw a case where LLPC was using that address space for an s_buffer_load, not an s_load. But I did not look into _why_ that was happening. I have never understood constant_32bit.

https://github.com/llvm/llvm-project/pull/91327