Forward port mem stuff to ch21

Also a minor reg-alloc improvement for BrainFuck, ported up to ch25

6 files changed, 47 insertions, 9 deletions

diff --git a/chapter23/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java b/chapter23/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
index 11c9409d..793732b4 100644
--- a/chapter23/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
+++ b/chapter23/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
@@ -591,8 +591,8 @@ public class RegAlloc {
                 if( defreg != usereg && splitBypass(bb,j,n,defreg) )
                     usereg = lrg(n.in(1))._reg;
 
-                // Split has same reg?  Useless!  Can remove it!
-                if( defreg == usereg ) {
+                // Same register, or the next instruction can use the source directly.
+                if( defreg == usereg || splitForward(bb,j,n,usereg) ) {
                     n.removeSplit();
                     j--;
                     continue;
@@ -605,6 +605,18 @@ public class RegAlloc {
         }
     }
 
+    // A sole, adjacent use can read the source register directly.  Nothing can
+    // clobber it in between; only the operand mask and two-address tie remain.
+    private boolean splitForward( CFGNode bb, int j, Node split, int reg ) {
+        if( split.nOuts()!=1 || j+1==bb.nOuts() ) return false;
+        Node use = split.out(0);
+        if( use!=bb.out(j+1) || use instanceof PhiNode || use instanceof CFGNode ||
+            !(use instanceof MachNode mach) ) return false;
+        int i = use._inputs.find(split);
+        RegMask mask = mach.regmap(i);
+        return mask!=null && mask.test(reg) && mach.twoAddress()!=i;
+    }
+
     private boolean splitBypass( CFGNode bb, int j, Node lo, int defreg ) {
         // Attempt to bypass split
         Node hi = lo.in(1);
diff --git a/chapter23/src/test/java/com/seaofnodes/simple/Chapter20Test.java b/chapter23/src/test/java/com/seaofnodes/simple/Chapter20Test.java
index 044ad4ed..d0c48688 100644
--- a/chapter23/src/test/java/com/seaofnodes/simple/Chapter20Test.java
+++ b/chapter23/src/test/java/com/seaofnodes/simple/Chapter20Test.java
@@ -115,7 +115,7 @@ val sqrt = { int x ->
 };
 return sqrt(arg) + sqrt(arg+2);
 """;
-        testTarget(src,"x86_64_v2", "SystemV",48,null);
+        testTarget(src,"x86_64_v2", "SystemV",40,null);
         testTarget(src,"riscv"    , "SystemV",17,null);
         testTarget(src,"arm"      , "SystemV",18,null);
     }
@@ -162,7 +162,7 @@ for( int i=0; i<ary#-1; i++ )
     ary[i+1] += ary[i];
 return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
 """;
-        testTarget(src,"x86_64_v2", "SystemV",9,"return .[];");
+        testTarget(src,"x86_64_v2", "SystemV",7,"return .[];");
         testTarget(src,"riscv"    , "SystemV",7,"return (add,.[],(mul,.[],1000));");
         testTarget(src,"arm"      , "SystemV",5,"return (add,.[],(mul,.[],1000));");
     }
@@ -207,7 +207,7 @@ hashCode(s);
 """;
         testTarget(src,"x86_64_v2", "SystemV",9,null);
         testTarget(src,"riscv"    , "SystemV",4,null);
-        testTarget(src,"arm"      , "SystemV",3,null);
+        testTarget(src,"arm"      , "SystemV",1,null);
     }
 
     @Test
diff --git a/chapter23/src/test/java/com/seaofnodes/simple/Chapter21AllocTest.java b/chapter23/src/test/java/com/seaofnodes/simple/Chapter21AllocTest.java
index 2d0493e5..bab7a86a 100644
--- a/chapter23/src/test/java/com/seaofnodes/simple/Chapter21AllocTest.java
+++ b/chapter23/src/test/java/com/seaofnodes/simple/Chapter21AllocTest.java
@@ -21,7 +21,7 @@ val sqrt = { int x ->
 };
 return sqrt(arg) + sqrt(arg+2);
 """;
-        Chapter21Test.testCPU(src,"x86_64_v2", "Win64"  ,48,null);
+        Chapter21Test.testCPU(src,"x86_64_v2", "Win64"  ,40,null);
         Chapter21Test.testCPU(src,"riscv"    , "SystemV",19,null);
         Chapter21Test.testCPU(src,"arm"      , "SystemV",19,null);
     }
@@ -49,7 +49,7 @@ return sqrt(arg) + sqrt(arg+2);
         String src = Files.readString(Path.of("src/test/java/com/seaofnodes/simple/progs/stringHash21.smp"));
         Chapter21Test.testCPU(src,"x86_64_v2", "SystemV", 9,null);
         Chapter21Test.testCPU(src,"riscv"    , "SystemV", 3,null);
-        Chapter21Test.testCPU(src,"arm"      , "SystemV", 3,null);
+        Chapter21Test.testCPU(src,"arm"      , "SystemV", 1,null);
     }
 
 }
diff --git a/chapter23/src/test/java/com/seaofnodes/simple/Chapter21Test.java b/chapter23/src/test/java/com/seaofnodes/simple/Chapter21Test.java
index 6438801b..14f9fdb8 100644
--- a/chapter23/src/test/java/com/seaofnodes/simple/Chapter21Test.java
+++ b/chapter23/src/test/java/com/seaofnodes/simple/Chapter21Test.java
@@ -196,6 +196,7 @@ public class Chapter21Test {
 
 
     @Test public void testCoalescing() { com.seaofnodes.simple.codegen.RegAllocTestSupport.coalescing(); }
+    @Test public void testCopyForward() throws Exception { com.seaofnodes.simple.codegen.RegAllocTestSupport.copyForward(); }
 
     @Test public void testNarrowStores() throws IOException {
         for( String type : new String[]{"i8","u8","i16","u16"} ) {
@@ -339,7 +340,7 @@ public class Chapter21Test {
         String src = Files.readString(Path.of("src/test/java/com/seaofnodes/simple/progs/stringHash.smp"));
         testCPU(src,"x86_64_v2", "SystemV", 9,null);
         testCPU(src,"riscv"    , "SystemV", 3,null);
-        testCPU(src,"arm"      , "SystemV", 3,null);
+        testCPU(src,"arm"      , "SystemV", 1,null);
     }
 
     @Test public void testStringExport() throws IOException {
diff --git a/chapter23/src/test/java/com/seaofnodes/simple/Chapter23AllocTest.java b/chapter23/src/test/java/com/seaofnodes/simple/Chapter23AllocTest.java
index cd8c43cf..7f4b86d5 100644
--- a/chapter23/src/test/java/com/seaofnodes/simple/Chapter23AllocTest.java
+++ b/chapter23/src/test/java/com/seaofnodes/simple/Chapter23AllocTest.java
@@ -11,7 +11,7 @@ public class Chapter23AllocTest {
         String src = Files.readString(Path.of("src/test/java/com/seaofnodes/simple/progs/stringHash.smp"));
         Chapter23Test.testCPU(src,"x86_64_v2", "SystemV", 9,null);
         Chapter23Test.testCPU(src,"riscv"    , "SystemV", 3,null);
-        Chapter23Test.testCPU(src,"arm"      , "SystemV", 3,null);
+        Chapter23Test.testCPU(src,"arm"      , "SystemV", 1,null);
     }
 
     @Test
diff --git a/chapter23/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java b/chapter23/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java
index f0830f1b..5b61d3b3 100644
--- a/chapter23/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java
+++ b/chapter23/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java
@@ -219,6 +219,31 @@ public class RegAllocTestSupport {
         assertFalse("A fixed definition clobbers even before coloring",uncolored.sameBlockNoClobber(copy));
     }
 
+    public static void copyForward() throws Exception {
+        // Forwarding, fixed operand, two-address tie, intervening clobber,
+        // another user, and a scheduling-only edge.
+        for( int kind=0; kind<6; kind++ ) {
+            CodeGen code = graph();
+            RegAlloc alloc = new RegAlloc(code);
+            Op def = new Op(A,null,null,false,code._start);
+            alloc.newLRG(def)._reg=0;
+            SplitNode copy = code._mach.split("test",(byte)0,null);
+            copy.setDef(0,code._start); copy.setDef(1,def);
+            alloc.newLRG(copy)._reg=1;
+            if( kind==3 ) new Op(null,null,A,false,code._start);
+            int twoAddress = kind==2 ? 1 : 0;
+            RegMask mask = kind==1 ? B : kind==5 ? null : new RegMask(3L);
+            Op use = new Op(null,mask,null,false,code._start,copy) {
+                @Override public int twoAddress() { return twoAddress; }
+            };
+            if( kind==4 ) new Op(null,B,null,false,code._start,copy);
+            var post = RegAlloc.class.getDeclaredMethod("postColor");
+            post.setAccessible(true); post.invoke(alloc);
+            assertSame("copy case "+kind,kind==0 ? def : copy,use.in(1));
+            assertEquals(kind==0 ? 0 : 1,alloc._spills);
+        }
+    }
+
     public static void coalescing() {
         // Merge, incompatible masks, interference, capacity, and adjacency remapping.
         for( int kind=0; kind<5; kind++ ) {