From 5f56f8125122353475fccb6da6f96ca63cea5298 Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <jolesen@mozilla.com>
Date: Fri, 29 Sep 2017 15:54:06 -0700
Subject: [PATCH] Resolve all value aliases when computing live ranges.

Value aliases are only in the way during register allocation, so make
sure they are all dead as we enter the register allocation passes.
---
 cranelift/filetests/regalloc/aliases.cton | 36 +++++++++++++++++++++++
 lib/cretonne/src/regalloc/liveness.rs     |  5 +++-
 2 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 cranelift/filetests/regalloc/aliases.cton

diff --git a/cranelift/filetests/regalloc/aliases.cton b/cranelift/filetests/regalloc/aliases.cton
new file mode 100644
index 0000000000..575fedd923
--- /dev/null
+++ b/cranelift/filetests/regalloc/aliases.cton
@@ -0,0 +1,36 @@
+test compile
+set is_64bit
+isa intel haswell
+
+function %value_aliases(i32, f32, i64 vmctx) spiderwasm {
+    gv0 = vmctx
+    heap0 = static gv0, min 0x0001_0000, bound 0x0001_0000_0000, guard 0x8000_0000
+
+ebb0(v0: i32, v1: f32, v2: i64):
+    v3 = iconst.i32 0
+    jump ebb3(v3)
+
+ebb3(v4: i32):
+    v5 = heap_addr.i64 heap0, v4, 1
+    v6 = load.f32 v5
+    v7 -> v1
+    v8 = fdiv v6, v7
+    v9 = heap_addr.i64 heap0, v4, 1
+    store v8, v9
+    v10 = iconst.i32 4
+    v11 = iadd v4, v10
+    v12 -> v0
+    v13 = icmp ult v11, v12
+    v14 = bint.i32 v13
+    brnz v14, ebb3(v11)
+    jump ebb4
+
+ebb4:
+    jump ebb2
+
+ebb2:
+    jump ebb1
+
+ebb1:
+    return
+}
diff --git a/lib/cretonne/src/regalloc/liveness.rs b/lib/cretonne/src/regalloc/liveness.rs
index 8faa8131c6..5dd6ce71bb 100644
--- a/lib/cretonne/src/regalloc/liveness.rs
+++ b/lib/cretonne/src/regalloc/liveness.rs
@@ -366,7 +366,7 @@ impl Liveness {
 
     /// Compute the live ranges of all SSA values used in `func`.
     /// This clears out any existing analysis stored in this data structure.
-    pub fn compute(&mut self, isa: &TargetIsa, func: &Function, cfg: &ControlFlowGraph) {
+    pub fn compute(&mut self, isa: &TargetIsa, func: &mut Function, cfg: &ControlFlowGraph) {
         self.ranges.clear();
 
         // Get ISA data structures used for computing live range affinities.
@@ -386,6 +386,9 @@ impl Liveness {
             }
 
             for inst in func.layout.ebb_insts(ebb) {
+                // Eliminate all value aliases, they would confuse the register allocator.
+                func.dfg.resolve_aliases_in_arguments(inst);
+
                 // Make sure we have created live ranges for dead defs.
                 // TODO: When we implement DCE, we can use the absence of a live range to indicate
                 // an unused value.