Hoist vector slices using rewrite rules

src/Simplify_Add.cpp

@@ -113,6 +113,9 @@ Expr Simplify::visit(const Add *op, ExprInfo *bounds) {
              rewrite(x*c0 + y*c1, (x + y*fold(c1/c0)) * c0, c1 % c0 == 0) ||
              rewrite(x*c0 + y*c1, (x*fold(c0/c1) + y) * c1, c0 % c1 == 0) ||
 
+             // Hoist shuffles. The Shuffle visitor wants to sink
+             // extract_elements to the leaves, and those count as degenerate
+             // shuffles, so only hoist shuffles that grab more than one lane.
              rewrite(slice(x, c0, c1, c2) + slice(y, c0, c1, c2), slice(x + y, c0, c1, c2), c2 > 1) ||
              rewrite(slice(x, c0, c1, c2) + (z + slice(y, c0, c1, c2)), slice(x + y, c0, c1, c2) + z, c2 > 1) ||
              rewrite(slice(x, c0, c1, c2) + (slice(y, c0, c1, c2) + z), slice(x + y, c0, c1, c2) + z, c2 > 1) ||

src/Simplify_Max.cpp

@@ -189,6 +189,9 @@ Expr Simplify::visit(const Max *op, ExprInfo *bounds) {
 
              rewrite(max(select(x, y, z), select(x, w, u)), select(x, max(y, w), max(z, u))) ||
 
+             // Hoist shuffles. The Shuffle visitor wants to sink
+             // extract_elements to the leaves, and those count as degenerate
+             // shuffles, so only hoist shuffles that grab more than one lane.
              rewrite(max(slice(x, c0, c1, c2), slice(y, c0, c1, c2)), slice(max(x, y), c0, c1, c2), c2 > 1) ||
              rewrite(max(slice(x, c0, c1, c2), max(slice(y, c0, c1, c2), z)), max(slice(max(x, y), c0, c1, c2), z), c2 > 1) ||
              rewrite(max(slice(x, c0, c1, c2), max(z, slice(y, c0, c1, c2))), max(slice(max(x, y), c0, c1, c2), z), c2 > 1) ||

src/Simplify_Min.cpp

@@ -193,6 +193,9 @@ Expr Simplify::visit(const Min *op, ExprInfo *bounds) {
 
              rewrite(min(select(x, y, z), select(x, w, u)), select(x, min(y, w), min(z, u))) ||
 
+             // Hoist shuffles. The Shuffle visitor wants to sink
+             // extract_elements to the leaves, and those count as degenerate
+             // shuffles, so only hoist shuffles that grab more than one lane.
              rewrite(min(slice(x, c0, c1, c2), slice(y, c0, c1, c2)), slice(min(x, y), c0, c1, c2), c2 > 1) ||
              rewrite(min(slice(x, c0, c1, c2), min(slice(y, c0, c1, c2), z)), min(slice(min(x, y), c0, c1, c2), z), c2 > 1) ||
              rewrite(min(slice(x, c0, c1, c2), min(z, slice(y, c0, c1, c2))), min(slice(min(x, y), c0, c1, c2), z), c2 > 1) ||

src/Simplify_Mul.cpp

@@ -95,6 +95,9 @@ Expr Simplify::visit(const Mul *op, ExprInfo *bounds) {
             rewrite(ramp(broadcast(x, c0), broadcast(y, c0), c1) * broadcast(z, c2),
                     ramp(broadcast(x * z, c0), broadcast(y * z, c0), c1), c2 == c0 * c1) ||
 
+            // Hoist shuffles. The Shuffle visitor wants to sink
+            // extract_elements to the leaves, and those count as degenerate
+            // shuffles, so only hoist shuffles that grab more than one lane.
             rewrite(slice(x, c0, c1, c2) * slice(y, c0, c1, c2), slice(x * y, c0, c1, c2), c2 > 1) ||
             rewrite(slice(x, c0, c1, c2) * (slice(y, c0, c1, c2) * z), slice(x * y, c0, c1, c2) * z, c2 > 1) ||
             rewrite(slice(x, c0, c1, c2) * (z * slice(y, c0, c1, c2)), slice(x * y, c0, c1, c2) * z, c2 > 1) ||

src/Simplify_Sub.cpp

@@ -175,6 +175,9 @@ Expr Simplify::visit(const Sub *op, ExprInfo *bounds) {
              rewrite(x - x%c0, (x/c0)*c0) ||
              rewrite(x - ((x + c0)/c1)*c1, (x + c0)%c1 - c0, c1 > 0) ||
 
+             // Hoist shuffles. The Shuffle visitor wants to sink
+             // extract_elements to the leaves, and those count as degenerate
+             // shuffles, so only hoist shuffles that grab more than one lane.
              rewrite(slice(x, c0, c1, c2) - slice(y, c0, c1, c2), slice(x - y, c0, c1, c2), c2 > 1) ||
              rewrite(slice(x, c0, c1, c2) - (z + slice(y, c0, c1, c2)), slice(x - y, c0, c1, c2) - z, c2 > 1) ||
              rewrite(slice(x, c0, c1, c2) - (slice(y, c0, c1, c2) + z), slice(x - y, c0, c1, c2) - z, c2 > 1) ||