[Valgrind-developers] [valgrind] Constant folding for Iop_Shl8/16, Iop_Shr8/16 and Iop_Sar8/16. (BZ 506211)

[Florian K. <fk...@so...>]

https://sourceware.org/cgit/valgrind/commit/?id=92b886de45265ca15e87f67d4245d77f292de80e

commit 92b886de45265ca15e87f67d4245d77f292de80e
Author: Florian Krohm <fl...@ei...>
Date:   Thu Jul 17 07:04:03 2025 +0000

    Constant folding for Iop_Shl8/16, Iop_Shr8/16 and Iop_Sar8/16. (BZ 506211)
    
    Part of fixing https://bugs.kde.org/show_bug.cgi?id=506211

Diff:
---
 VEX/priv/ir_opt.c               | 56 +++++++++++++++++++++++++++++++++++++++++
 none/tests/iropt-test/binary.c  | 16 ++++++++----
 none/tests/iropt-test/irops.tab | 12 ++++-----
 3 files changed, 73 insertions(+), 11 deletions(-)

diff --git a/VEX/priv/ir_opt.c b/VEX/priv/ir_opt.c
index 91b266aa1d..4653704d3e 100644
--- a/VEX/priv/ir_opt.c
+++ b/VEX/priv/ir_opt.c
@@ -2093,6 +2093,22 @@ static IRExpr* fold_Expr_WRK ( IRExpr** env, IRExpr* e )
             }
 
             /* -- Shl -- */
+            case Iop_Shl8:
+               vassert(e->Iex.Binop.arg2->Iex.Const.con->tag == Ico_U8);
+               shift = e->Iex.Binop.arg2->Iex.Const.con->Ico.U8;
+               if (shift >= 0 && shift <= 7)
+                  e2 = IRExpr_Const(IRConst_U8(toUChar(
+                          (e->Iex.Binop.arg1->Iex.Const.con->Ico.U8
+                           << shift))));
+               break;
+            case Iop_Shl16:
+               vassert(e->Iex.Binop.arg2->Iex.Const.con->tag == Ico_U8);
+               shift = e->Iex.Binop.arg2->Iex.Const.con->Ico.U8;
+               if (shift >= 0 && shift <= 15)
+                  e2 = IRExpr_Const(IRConst_U16(toUShort(
+                          (e->Iex.Binop.arg1->Iex.Const.con->Ico.U16
+                           << shift))));
+               break;
             case Iop_Shl32:
                vassert(e->Iex.Binop.arg2->Iex.Const.con->tag == Ico_U8);
                shift = (Int)(e->Iex.Binop.arg2->Iex.Const.con->Ico.U8);
@@ -2111,6 +2127,28 @@ static IRExpr* fold_Expr_WRK ( IRExpr** env, IRExpr* e )
                break;
 
             /* -- Sar -- */
+            case Iop_Sar8: {
+               Int s8;
+               vassert(e->Iex.Binop.arg2->Iex.Const.con->tag == Ico_U8);
+               s8    = (Char)(e->Iex.Binop.arg1->Iex.Const.con->Ico.U8);
+               shift = e->Iex.Binop.arg2->Iex.Const.con->Ico.U8;
+               if (shift >= 0 && shift <= 7) {
+                  s8 >>=/*signed*/ shift;
+                  e2 = IRExpr_Const(IRConst_U8(toUChar(s8)));
+               }
+               break;
+            }
+            case Iop_Sar16: {
+               Int s16;
+               vassert(e->Iex.Binop.arg2->Iex.Const.con->tag == Ico_U8);
+               s16   = (Short)(e->Iex.Binop.arg1->Iex.Const.con->Ico.U16);
+               shift = e->Iex.Binop.arg2->Iex.Const.con->Ico.U8;
+               if (shift >= 0 && shift <= 15) {
+                  s16 >>=/*signed*/ shift;
+                  e2 = IRExpr_Const(IRConst_U16(toUShort(s16)));
+               }
+               break;
+            }
             case Iop_Sar32: {
                /* paranoid ... */
                /*signed*/ Int s32;
@@ -2137,6 +2175,24 @@ static IRExpr* fold_Expr_WRK ( IRExpr** env, IRExpr* e )
             }
 
             /* -- Shr -- */
+            case Iop_Shr8: {
+               vassert(e->Iex.Binop.arg2->Iex.Const.con->tag == Ico_U8);
+               shift = e->Iex.Binop.arg2->Iex.Const.con->Ico.U8;
+               if (shift >= 0 && shift <= 7)
+                  e2 = IRExpr_Const(IRConst_U8(toUChar(
+                          (e->Iex.Binop.arg1->Iex.Const.con->Ico.U8
+                           >> shift))));
+               break;
+            }
+            case Iop_Shr16: {
+               vassert(e->Iex.Binop.arg2->Iex.Const.con->tag == Ico_U8);
+               shift = e->Iex.Binop.arg2->Iex.Const.con->Ico.U8;
+               if (shift >= 0 && shift <= 15)
+                  e2 = IRExpr_Const(IRConst_U16(toUShort(
+                          (e->Iex.Binop.arg1->Iex.Const.con->Ico.U16
+                           >> shift))));
+               break;
+            }
             case Iop_Shr32: {
                /* paranoid ... */
                /*unsigned*/ UInt u32;
diff --git a/none/tests/iropt-test/binary.c b/none/tests/iropt-test/binary.c
index 894213a569..2c815c8136 100644
--- a/none/tests/iropt-test/binary.c
+++ b/none/tests/iropt-test/binary.c
@@ -148,20 +148,26 @@ check_result(const irop_t *op, const test_data_t *data)
       expected = (int64_t)(int32_t)opnd_l * (int64_t)(int32_t)opnd_r;
       break;
 
+   case Iop_Shl8:
+   case Iop_Shl16:
    case Iop_Shl32:
-      expected = opnd_l << opnd_r;
-      break;
-
    case Iop_Shl64:
       expected = opnd_l << opnd_r;
       break;
 
+   case Iop_Shr8:
+   case Iop_Shr16:
    case Iop_Shr32:
+   case Iop_Shr64:
       expected = opnd_l >> opnd_r;
       break;
 
-   case Iop_Shr64:
-      expected = opnd_l >> opnd_r;
+   case Iop_Sar8:
+      expected = ((int64_t)(opnd_l << 56) >> 56) >> opnd_r;
+      break;
+
+   case Iop_Sar16:
+      expected = ((int64_t)(opnd_l << 48) >> 48) >> opnd_r;
       break;
 
    case Iop_Sar32:
diff --git a/none/tests/iropt-test/irops.tab b/none/tests/iropt-test/irops.tab
index a9f57a4ce1..efae871fbf 100644
--- a/none/tests/iropt-test/irops.tab
+++ b/none/tests/iropt-test/irops.tab
@@ -164,18 +164,18 @@
 // { OPNAME(ModU128), Ity_I128, 2, Ity_I128, Ity_I128 }, // 128 bit
 // { OPNAME(ModS128), Ity_I128, 2, Ity_I128, Ity_I128 }, // 128 bit
 
-// { OPNAME(Shl8),  Ity_I8,  2, Ity_I8,  Ity_I8 },  // no folding yet
-// { OPNAME(Shl16), Ity_I16, 2, Ity_I16, Ity_I8 },  // no folding yet
+   { OPNAME(Shl8),  Ity_I8,  2, Ity_I8,  Ity_I8 },
+   { OPNAME(Shl16), Ity_I16, 2, Ity_I16, Ity_I8 },
    { OPNAME(Shl32), Ity_I32, 2, Ity_I32, Ity_I8 },
    { OPNAME(Shl64), Ity_I64, 2, Ity_I64, Ity_I8 },
 
-// { OPNAME(Shr8),  Ity_I8,  2, Ity_I8,  Ity_I8 },  // no folding yet
-// { OPNAME(Shr16), Ity_I16, 2, Ity_I16, Ity_I8 },  // no folding yet
+   { OPNAME(Shr8),  Ity_I8,  2, Ity_I8,  Ity_I8 },
+   { OPNAME(Shr16), Ity_I16, 2, Ity_I16, Ity_I8 },
    { OPNAME(Shr32), Ity_I32, 2, Ity_I32, Ity_I8 },
    { OPNAME(Shr64), Ity_I64, 2, Ity_I64, Ity_I8 },
 
-// { OPNAME(Sar8),  Ity_I8,  2, Ity_I8,  Ity_I8 },  // no folding yet
-// { OPNAME(Sar16), Ity_I16, 2, Ity_I16, Ity_I8 },  // no folding yet
+   { OPNAME(Sar8),  Ity_I8,  2, Ity_I8,  Ity_I8 },
+   { OPNAME(Sar16), Ity_I16, 2, Ity_I16, Ity_I8 },
    { OPNAME(Sar32), Ity_I32, 2, Ity_I32, Ity_I8 },
    { OPNAME(Sar64), Ity_I64, 2, Ity_I64, Ity_I8 },