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From: Xi Ruoyao <xry111@xry111.site>
To: chenglulu <chenglulu@loongson.cn>, gcc-patches@gcc.gnu.org
Cc: i@xen0n.name, xuchenghua@loongson.cn
Subject: Re: [PATCH v2 2/2] LoongArch: When the code model is extreme, the symbol address is obtained through macro instructions regardless of the value of -mexplicit-relocs.
Date: Fri, 05 Jan 2024 22:16:25 +0800	[thread overview]
Message-ID: <cf7d86a706767eeecfa39efaff450f58d3da876e.camel@xry111.site> (raw)
In-Reply-To: <a5585703-25d7-2abc-7dd1-f4806afe8cfb@loongson.cn>

On Fri, 2024-01-05 at 20:45 +0800, chenglulu wrote:
> 
> 在 2024/1/5 下午7:55, Xi Ruoyao 写道:
> > On Fri, 2024-01-05 at 18:25 +0800, Xi Ruoyao wrote:
> > > On Fri, 2024-01-05 at 17:57 +0800, chenglulu wrote:
> > > > 在 2024/1/5 下午4:37, Xi Ruoyao 写道:
> > > > > On Fri, 2024-01-05 at 11:40 +0800, Lulu Cheng wrote:
> > > > > >    bool
> > > > > >    loongarch_explicit_relocs_p (enum loongarch_symbol_type type)
> > > > > >    {
> > > > > > +  /* Instructions pcalau12i, addi.d, lu32i.d and lu52i.d must be adjancent
> > > > > > +     so that the linker can infer the PC of pcalau12i to apply relocations
> > > > > > +     to lu32i.d and lu52i.d.  Otherwise, the results would be incorrect if
> > > > > > +     these four instructions are not in the same 4KiB page.
> > > > > > +     Therefore, macro instructions are used when cmodel=extreme.  */
> > > > > > +  if (loongarch_symbol_extreme_p (type))
> > > > > > +    return false;
> > > > > I think this is a bit of strange.  With -mexplicit-relocs={auto,always}
> > > > > we should still use explicit relocs, but coding all 4 instructions
> > > > > altogether as
> > > > > 
> > > > > "pcalau12i.d\t%1,%pc64_hi12(%2)\n\taddi.d\t%0,$r0,%pclo12(%2)\n\tlu32i.d\t%0,%pc64_lo20(%2)\n\tlu52i.d\t%0,%0,%pc64_hi12(%2)"
> > > > > 
> > > > > Give me several hours trying to implement this...
> > > > > 
> > > > I think there is no difference between macros and these instructions put
> > > > together. If implement it in a split form, I think I can try it through
> > > > TARGET_SCHED_MACRO_FUSION_PAIR_P
> > We don't need to split the insn.  We can just add a "large insn"
> > containing the assembly output we want.
> > 
> > See the attached patch.  Note that TLS LE/LD/GD needs a fix too because
> > they are basically an variation of GOT addressing.
> > 
> > I've ran some small tests and now trying to bootstrap GCC with -
> > mcmodel=extreme in BOOT_CFLAGS...
> > 
> > > There is a difference:
> > > 
> > > int x;
> > > int t() { return x; }
> > > 
> > > pcalau12i.d t0, %pc_hi20(x)
> > > addi.d t1, r0, %pc_lo12(x)
> > > lu32i.d t1, %pc64_lo20(x)
> > > lu52i.d t1, t1, %pc64_hi12(x)
> > > ldx.w a0, t0, t1
> > > 
> > > is slightly better than
> > > 
> > > pcalau12i.d t0, %pc_hi20(x)
> > > addi.d t1, r0, %pc_lo12(x)
> > > lu32i.d t1, %pc64_lo20(x)
> > > lu52i.d t1, t1, %pc64_hi12(x)
> > > addi.d t0, t0, t1
> > > ld.w a0, t0, 0
> > > 
> > > And generating macros when -mexplicit-relocs=always can puzzle people
> > > (it says "always" :-\ ).
> > > 
> Thumbs up! This method is much better than my method, I learned 
> something! grateful!
> But I still have to test the accuracy.

I found an issue bootstrapping GCC with -mcmodel=extreme in BOOT_CFLAGS:
we need a target hook to tell the generic code
UNSPEC_LA_PCREL_64_PART{1,2} are just a wrapper around symbols, or we'll
see millions lines of messages like

../../gcc/gcc/tree.h:4171:1: note: non-delegitimized UNSPEC
UNSPEC_LA_PCREL_64_PART1 (42) found in variable location

diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index 4f89c4af323..410e1b5e693 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -10868,6 +10868,24 @@ loongarch_asm_code_end (void)
 #undef DUMP_FEATURE
 }
 
+static rtx loongarch_delegitimize_address (rtx op)
+{
+  if (GET_CODE (op) == UNSPEC)
+  {
+    int unspec = XINT (op, 1);
+    switch (unspec)
+      {
+      case UNSPEC_LA_PCREL_64_PART1:
+      case UNSPEC_LA_PCREL_64_PART2:
+	return XVECEXP (op, 0, 0);
+      default:
+	return op;
+      }
+  }
+
+  return op;
+}
+
 /* Initialize the GCC target structure.  */
 #undef TARGET_ASM_ALIGNED_HI_OP
 #define TARGET_ASM_ALIGNED_HI_OP "\t.half\t"
@@ -11129,6 +11147,10 @@ loongarch_asm_code_end (void)
 #define TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT \
   loongarch_builtin_support_vector_misalignment
 
+#undef TARGET_DELEGITIMIZE_ADDRESS
+#define TARGET_DELEGITIMIZE_ADDRESS \
+  loongarch_delegitimize_address
+
 struct gcc_target targetm = TARGET_INITIALIZER;
 
 #include "gt-loongarch.h"

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University

  reply	other threads:[~2024-01-05 14:16 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-01-05  3:40 [PATCH v2 0/2] When cmodel=extreme, add macro support and only support macros Lulu Cheng
2024-01-05  3:40 ` [PATCH v2 1/2] LoongArch: Add the macro implementation of mcmodel=extreme Lulu Cheng
2024-01-05  3:40 ` [PATCH v2 2/2] LoongArch: When the code model is extreme, the symbol address is obtained through macro instructions regardless of the value of -mexplicit-relocs Lulu Cheng
2024-01-05  8:37   ` Xi Ruoyao
2024-01-05  8:51     ` chenglulu
2024-01-05  9:57     ` chenglulu
2024-01-05 10:25       ` Xi Ruoyao
2024-01-05 11:55         ` Xi Ruoyao
2024-01-05 12:45           ` chenglulu
2024-01-05 14:16             ` Xi Ruoyao [this message]
2024-01-12  1:46               ` chenglulu
2024-01-12 11:42                 ` Xi Ruoyao
2024-01-13  7:01                   ` chenglulu
2024-01-13 13:05                     ` Xi Ruoyao
2024-01-13 14:05                       ` chenglulu
2024-01-17  9:38                       ` chenglulu
2024-01-17  9:50                         ` Xi Ruoyao
2024-01-17  9:57                           ` chenglulu
2024-01-19  5:46                             ` Xi Ruoyao
2024-01-19  8:51                               ` chenglulu
2024-01-22  7:27                                 ` chenglulu
2024-01-23 19:36                                   ` Xi Ruoyao
2024-01-25  0:48                                     ` chenglulu
2024-01-25  7:59                                       ` Xi Ruoyao

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