Add EntryRegDiversions to record diversions for each block entry.

cranelift/codegen/src/ir/function.rs

@@ -14,7 +14,7 @@ use crate::ir::{
 use crate::ir::{EbbOffsets, InstEncodings, SourceLocs, StackSlots, ValueLocations};
 use crate::ir::{JumpTableOffsets, JumpTables};
 use crate::isa::{CallConv, EncInfo, Encoding, Legalize, TargetIsa};
-use crate::regalloc::RegDiversions;
+use crate::regalloc::{EntryRegDiversions, RegDiversions};
 use crate::value_label::ValueLabelsRanges;
 use crate::write::write_function;
 use core::fmt;
@@ -62,6 +62,12 @@ pub struct Function {
     /// Location assigned to every value.
     pub locations: ValueLocations,
 
+    /// Non-default locations assigned to value at the entry of basic blocks.
+    ///
+    /// At the entry of each basic block, we might have values which are not in their default
+    /// ValueLocation. This field records these register-to-register moves as Diversions.
+    pub entry_diversions: EntryRegDiversions,
+
     /// Code offsets of the EBB headers.
     ///
     /// This information is only transiently available after the `binemit::relax_branches` function
@@ -94,6 +100,7 @@ impl Function {
             layout: Layout::new(),
             encodings: SecondaryMap::new(),
             locations: SecondaryMap::new(),
+            entry_diversions: EntryRegDiversions::new(),
             offsets: SecondaryMap::new(),
             jt_offsets: SecondaryMap::new(),
             srclocs: SecondaryMap::new(),
@@ -112,6 +119,7 @@ impl Function {
         self.layout.clear();
         self.encodings.clear();
         self.locations.clear();
+        self.entry_diversions.clear();
         self.offsets.clear();
         self.jt_offsets.clear();
         self.srclocs.clear();
@@ -198,10 +206,12 @@ impl Function {
             !self.offsets.is_empty(),
             "Code layout must be computed first"
         );
+        let mut divert = RegDiversions::new();
+        divert.at_ebb(&self.entry_diversions, ebb);
         InstOffsetIter {
             encinfo: encinfo.clone(),
             func: self,
-            divert: RegDiversions::new(),
+            divert,
             encodings: &self.encodings,
             offset: self.offsets[ebb],
             iter: self.layout.ebb_insts(ebb),