From: Florian Krohm <flo2030@eich-krohm.de>
Date: Thu, 31 Jul 2025 21:28:39 +0000 (+0000)
Subject: nanomips specific changes for BZ 507033
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a5c48217e94;p=thirdparty%2Fvalgrind.git

nanomips specific changes for BZ 507033

Rework code to use Iop_ClzNat32 instead of the deprecated Iop_Clz32.

Iop_Clz32 is used to implement the CLZ insn which behaves naturally
when the input is 0:  CLZ(0) == 32
So it seems as if using Iop_Clz32 is wrong because it has undefined
behaviour when the input value is 0. However, the VEX pipeline
does this:

CLZ insn --ir--> Iop_Clz32 --isel--> NMun_CLZ --emit--> CLZ

So it all works out. Essentially the semantics of Iop_Clz32 were
redefined to be like Iop_ClzNat32.

In IR generation we can drop the special handling for CLO(0) because
Iop_ClzNat32 takes care of that.

Part of fixing https://bugs.kde.org/show_bug.cgi?id=507033
---

diff --git a/VEX/priv/guest_nanomips_toIR.c b/VEX/priv/guest_nanomips_toIR.c
index 3827ac3fc..fddc1afa4 100644
--- a/VEX/priv/guest_nanomips_toIR.c
+++ b/VEX/priv/guest_nanomips_toIR.c
@@ -864,23 +864,17 @@ static void nano_pool32Axf_4(DisResult *dres, UInt cins)
 {
    UChar rs = (cins >> 16) & 0x1F;
    UChar rt = (cins >> 21) & 0x1F;
-   IRTemp t1;
 
    switch ((cins >> 9) & 0x7F) {
       case nano_POOL32Axf4_CLO: {  /* clo */
          DIP("clo r%u, r%u", rt, rs);
-         t1 = newTemp(Ity_I1);
-         assign(t1, binop(Iop_CmpEQ32, getIReg(rs), mkU32(0xffffffff)));
-         putIReg(rt, IRExpr_ITE(mkexpr(t1),
-                                mkU32(0x00000020),
-                                unop(Iop_Clz32,
-                                     unop(Iop_Not32, getIReg(rs)))));
+         putIReg(rt, unop(Iop_ClzNat32, unop(Iop_Not32, getIReg(rs))));
          break;
       }
 
       case nano_POOL32Axf4_CLZ: {  /* clz */
          DIP("clz r%u, r%u", rt, rs);
-         putIReg(rt, unop(Iop_Clz32, getIReg(rs)));
+         putIReg(rt, unop(Iop_ClzNat32, getIReg(rs)));
          break;
       }
    }
diff --git a/VEX/priv/host_nanomips_isel.c b/VEX/priv/host_nanomips_isel.c
index c4a8f4fe3..05e4cc512 100644
--- a/VEX/priv/host_nanomips_isel.c
+++ b/VEX/priv/host_nanomips_isel.c
@@ -815,7 +815,7 @@ static HReg iselWordExpr_R_wrk(ISelEnv * env, IRExpr * e)
                return r_dst;
             }
 
-            case Iop_Clz32: {
+            case Iop_ClzNat32: {
                HReg r_dst = newVRegI(env);
                HReg r_src = iselWordExpr_R(env, e->Iex.Unop.arg);
                addInstr(env, NANOMIPSInstr_Unary(NMun_CLZ, r_dst, r_src));