nir: Add a no wrapping bits to nir_alu_instr

They indicate the operation does not cause overflow or underflow.
This is motivated by SPIR-V decorations NoSignedWrap and
NoUnsignedWrap.

Change the storage of `exact` to be a single bit, so they pack
together.

v2: Handle no_wrap in nir_instr_set.  (Karol)

v3: Use two separate flags, since the NIR SSA values and certain
    instructions are typeless, so just no_wrap would be insufficient
    to know which one was referred to.  (Connor)

v4: Don't use nir_instr_set to propagate the flags, unlike `exact`,
    consider the instructions different if the flags have different
    values.  Fix hashing/comparing.  (Jason)

Reviewed-by: Karol Herbst <kherbst@redhat.com> [v1]
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/nir/nir.h

@@ -961,7 +961,14 @@ typedef struct nir_alu_instr {
     * it must ensure that the resulting value is bit-for-bit identical to the
     * original.
     */
-   bool exact;
+   bool exact:1;
+
+   /**
+    * Indicates that this instruction do not cause wrapping to occur, in the
+    * form of overflow or underflow.
+    */
+   bool no_signed_wrap:1;
+   bool no_unsigned_wrap:1;
 
    nir_alu_dest dest;
    nir_alu_src src[];

src/compiler/nir/nir_clone.c

@@ -290,6 +290,8 @@ clone_alu(clone_state *state, const nir_alu_instr *alu)
 {
    nir_alu_instr *nalu = nir_alu_instr_create(state->ns, alu->op);
    nalu->exact = alu->exact;
+   nalu->no_signed_wrap = alu->no_signed_wrap;
+   nalu->no_unsigned_wrap = alu->no_unsigned_wrap;
 
    __clone_dst(state, &nalu->instr, &nalu->dest.dest, &alu->dest.dest);
    nalu->dest.saturate = alu->dest.saturate;

src/compiler/nir/nir_instr_set.c

@@ -52,9 +52,14 @@ static uint32_t
 hash_alu(uint32_t hash, const nir_alu_instr *instr)
 {
    hash = HASH(hash, instr->op);
+
+   /* We explicitly don't hash instr->exact. */
+   uint8_t flags = instr->no_signed_wrap |
+                   instr->no_unsigned_wrap << 1;
+   hash = HASH(hash, flags);
+
    hash = HASH(hash, instr->dest.dest.ssa.num_components);
    hash = HASH(hash, instr->dest.dest.ssa.bit_size);
-   /* We explicitly don't hash instr->dest.dest.exact */
 
    if (nir_op_infos[instr->op].algebraic_properties & NIR_OP_IS_2SRC_COMMUTATIVE) {
       assert(nir_op_infos[instr->op].num_inputs >= 2);
@@ -523,6 +528,14 @@ nir_instrs_equal(const nir_instr *instr1, const nir_instr *instr2)
       if (alu1->op != alu2->op)
          return false;
 
+      /* We explicitly don't compare instr->exact. */
+
+      if (alu1->no_signed_wrap != alu2->no_signed_wrap)
+         return false;
+
+      if (alu1->no_unsigned_wrap != alu2->no_unsigned_wrap)
+         return false;
+
       /* TODO: We can probably acutally do something more inteligent such
        * as allowing different numbers and taking a maximum or something
        * here */
@@ -532,8 +545,6 @@ nir_instrs_equal(const nir_instr *instr1, const nir_instr *instr2)
       if (alu1->dest.dest.ssa.bit_size != alu2->dest.dest.ssa.bit_size)
          return false;
 
-      /* We explicitly don't hash instr->dest.dest.exact */
-
       if (nir_op_infos[alu1->op].algebraic_properties & NIR_OP_IS_2SRC_COMMUTATIVE) {
          if ((!nir_alu_srcs_equal(alu1, alu2, 0, 0) ||
               !nir_alu_srcs_equal(alu1, alu2, 1, 1)) &&

src/compiler/nir/nir_print.c

@@ -241,6 +241,10 @@ print_alu_instr(nir_alu_instr *instr, print_state *state)
       fprintf(fp, "!");
    if (instr->dest.saturate)
       fprintf(fp, ".sat");
+   if (instr->no_signed_wrap)
+      fprintf(fp, ".nsw");
+   if (instr->no_unsigned_wrap)
+      fprintf(fp, ".nuw");
    fprintf(fp, " ");
 
    for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) {

src/compiler/nir/nir_serialize.c

@@ -379,8 +379,10 @@ write_alu(write_ctx *ctx, const nir_alu_instr *alu)
 {
    blob_write_uint32(ctx->blob, alu->op);
    uint32_t flags = alu->exact;
-   flags |= alu->dest.saturate << 1;
-   flags |= alu->dest.write_mask << 2;
+   flags |= alu->no_signed_wrap << 1;
+   flags |= alu->no_unsigned_wrap << 2;
+   flags |= alu->dest.saturate << 3;
+   flags |= alu->dest.write_mask << 4;
    blob_write_uint32(ctx->blob, flags);
 
    write_dest(ctx, &alu->dest.dest);
@@ -403,8 +405,10 @@ read_alu(read_ctx *ctx)
 
    uint32_t flags = blob_read_uint32(ctx->blob);
    alu->exact = flags & 1;
-   alu->dest.saturate = flags & 2;
-   alu->dest.write_mask = flags >> 2;
+   alu->no_signed_wrap = flags & 2;
+   alu->no_unsigned_wrap = flags & 4;
+   alu->dest.saturate = flags & 8;
+   alu->dest.write_mask = flags >> 4;
 
    read_dest(ctx, &alu->dest.dest, &alu->instr);