[SPARC] Fix PR target/107248

[Eric Botcazou <botcazou@adacore.com>]

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This is the infamous PR rtl-optimization/38644 rearing its ugly head for leaf 
functions on SPARC more than a decade later...  Richard E.'s generic solution 
has never been implemented so let's do as other RISC back-ends did.

Tested on SPARC64/Linux, applied on all active branches.


2022-10-14  Eric Botcazou  <ebotcazou@adacore.com>

	PR target/107248
	* config/sparc/sparc.cc (sparc_expand_prologue): Emit a frame
	blockage for leaf functions.
	(sparc_flat_expand_prologue): Emit frame instead of full blockage.
	(sparc_expand_epilogue): Emit a frame blockage for leaf functions.
	(sparc_flat_expand_epilogue): Emit frame instead of full blockage.

-- 
Eric Botcazou

[-- Attachment #2: pr107248.diff --]
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diff --git a/gcc/config/sparc/sparc.cc b/gcc/config/sparc/sparc.cc
index c72c38e1999..10c0f52d3d9 100644
--- a/gcc/config/sparc/sparc.cc
+++ b/gcc/config/sparc/sparc.cc
@@ -6051,6 +6051,9 @@ sparc_expand_prologue (void)
 	}
 
       RTX_FRAME_RELATED_P (insn) = 1;
+
+      /* Ensure no memory access is done before the frame is established.  */
+      emit_insn (gen_frame_blockage ());
     }
   else
     {
@@ -6065,13 +6068,7 @@ sparc_expand_prologue (void)
 	  /* %sp is not the CFA register anymore.  */
 	  emit_insn (gen_stack_pointer_inc (GEN_INT (4096 - size)));
 
-	  /* Make sure no %fp-based store is issued until after the frame is
-	     established.  The offset between the frame pointer and the stack
-	     pointer is calculated relative to the value of the stack pointer
-	     at the end of the function prologue, and moving instructions that
-	     access the stack via the frame pointer between the instructions
-	     that decrement the stack pointer could result in accessing the
-	     register window save area, which is volatile.  */
+	  /* Likewise.  */
 	  emit_insn (gen_frame_blockage ());
 	}
       else
@@ -6167,8 +6164,8 @@ sparc_flat_expand_prologue (void)
 	}
       RTX_FRAME_RELATED_P (insn) = 1;
 
-      /* Ensure nothing is scheduled until after the frame is established.  */
-      emit_insn (gen_blockage ());
+      /* Ensure no memory access is done before the frame is established.  */
+      emit_insn (gen_frame_blockage ());
 
       if (frame_pointer_needed)
 	{
@@ -6255,6 +6252,9 @@ sparc_expand_epilogue (bool for_eh)
     ; /* do nothing.  */
   else if (sparc_leaf_function_p)
     {
+      /* Ensure no memory access is done after the frame is destroyed.  */
+      emit_insn (gen_frame_blockage ());
+
       if (size <= 4096)
 	emit_insn (gen_stack_pointer_inc (GEN_INT (size)));
       else if (size <= 8192)
@@ -6305,15 +6305,15 @@ sparc_flat_expand_epilogue (bool for_eh)
     ; /* do nothing.  */
   else if (frame_pointer_needed)
     {
-      /* Make sure the frame is destroyed after everything else is done.  */
-      emit_insn (gen_blockage ());
+      /* Ensure no memory access is done after the frame is destroyed.  */
+      emit_insn (gen_frame_blockage ());
 
       emit_move_insn (stack_pointer_rtx, gen_rtx_REG (Pmode, 1));
     }
   else
     {
       /* Likewise.  */
-      emit_insn (gen_blockage ());
+      emit_insn (gen_frame_blockage ());
 
       if (size <= 4096)
 	emit_insn (gen_stack_pointer_inc (GEN_INT (size)));