[llvm] [AMDGPU] Fix negative immediate offset for unbuffered smem loads (PR #89165)

[Matt Arsenault via llvm-commits]

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@@ -1985,35 +1985,47 @@ bool AMDGPUDAGToDAGISel::SelectScratchSVAddr(SDNode *N, SDValue Addr,
 // offsets available on CI.
 bool AMDGPUDAGToDAGISel::SelectSMRDOffset(SDValue ByteOffsetNode,
                                           SDValue *SOffset, SDValue *Offset,
-                                          bool Imm32Only, bool IsBuffer) const {
+                                          bool Imm32Only, bool IsBuffer,
+                                          bool HasSOffset,
+                                          int64_t ImmOffset) const {
   assert((!SOffset || !Offset) &&
          "Cannot match both soffset and offset at the same time!");
 
   ConstantSDNode *C = dyn_cast<ConstantSDNode>(ByteOffsetNode);
   if (!C) {
     if (!SOffset)
       return false;
+    bool Changed = false;
     if (ByteOffsetNode.getValueType().isScalarInteger() &&
         ByteOffsetNode.getValueType().getSizeInBits() == 32) {
       *SOffset = ByteOffsetNode;
-      return true;
-    }
-    if (ByteOffsetNode.getOpcode() == ISD::ZERO_EXTEND) {
+      Changed = true;
+    } else if (ByteOffsetNode.getOpcode() == ISD::ZERO_EXTEND) {
       if (ByteOffsetNode.getOperand(0).getValueType().getSizeInBits() == 32) {
         *SOffset = ByteOffsetNode.getOperand(0);
-        return true;
+        Changed = true;
       }
     }
-    return false;
+    // For unbuffered smem loads, it is illegal for the Immediate Offset to be
+    // negative if the resulting (Offset + (M0 or SOffset or zero) is negative.
+    // Handle the case where the Immediate Offset + SOffset is negative.
+    if (AMDGPU::hasSMRDSignedImmOffset(*Subtarget) && Changed &&
+        !IsBuffer & !Imm32Only && ImmOffset < 0) {
+      KnownBits SKnown = CurDAG->computeKnownBits(*SOffset);
+      if (ImmOffset + SKnown.getMinValue().getSExtValue() < 0)
+        return false;
+    }
+
+    return Changed;
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arsenm wrote:

always true 

https://github.com/llvm/llvm-project/pull/89165