JIT: don't forward sub a volatile read tree via copy (#62224)

AndyAyersMS · web-flow · commit 2a8006695469 · 2021-12-01T18:34:46.000-08:00
The copy may not get the same value as the original. Detect this by looking for `GTF_ORDER_SIDEEFF`. Closes #62048.
diff --git a/src/coreclr/jit/redundantbranchopts.cpp b/src/coreclr/jit/redundantbranchopts.cpp
@@ -907,13 +907,13 @@ bool Compiler::optRedundantRelop(BasicBlock* const block)
             continue;
         }
 
-        // If prevTree has side effects other than GTF_EXCEPT or GTF_ASG, bail,
+        // If prevTree has side effects, bail,
         // unless it is in the immediately preceeding statement.
         //
         // (we'll later show that any exception must come from the RHS as the LHS
         // will be a simple local).
         //
-        if ((prevTree->gtFlags & GTF_SIDE_EFFECT) != (prevTree->gtFlags & (GTF_EXCEPT | GTF_ASG)))
+        if ((prevTree->gtFlags & (GTF_CALL | GTF_ORDER_SIDEEFF)) != 0)
         {
             if (prevStmt->GetNextStmt() != stmt)
             {

Original file line number	Diff line number	Diff line change
`@@ -907,13 +907,13 @@ bool Compiler::optRedundantRelop(BasicBlock* const block)`
`907`	`907`	`continue;`
`908`	`908`	`}`
`909`	`909`
`910`		`- // If prevTree has side effects other than GTF_EXCEPT or GTF_ASG, bail,`
	`910`	`+ // If prevTree has side effects, bail,`
`911`	`911`	`// unless it is in the immediately preceeding statement.`
`912`	`912`	`//`
`913`	`913`	`// (we'll later show that any exception must come from the RHS as the LHS`
`914`	`914`	`// will be a simple local).`
`915`	`915`	`//`
`916`		`- if ((prevTree->gtFlags & GTF_SIDE_EFFECT) != (prevTree->gtFlags & (GTF_EXCEPT \| GTF_ASG)))`
	`916`	`+ if ((prevTree->gtFlags & (GTF_CALL \| GTF_ORDER_SIDEEFF)) != 0)`
`917`	`917`	`{`
`918`	`918`	`if (prevStmt->GetNextStmt() != stmt)`
`919`	`919`	`{`