Index: gcc/config/i386/i386.md
===================================================================
--- gcc/config/i386/i386.md	(revision 128981)
+++ gcc/config/i386/i386.md	(working copy)
@@ -18699,7 +18699,9 @@ (define_expand "strmov"
   operands[5] = gen_rtx_PLUS (Pmode, operands[0], adjust);
   operands[6] = gen_rtx_PLUS (Pmode, operands[2], adjust);
 
-  if (TARGET_SINGLE_STRINGOP || optimize_size)
+  /* Can't use this if the user has appropriated esi or edi.  */
+  if ((TARGET_SINGLE_STRINGOP || optimize_size)
+      && !(global_regs[4] || global_regs[5]))
     {
       emit_insn (gen_strmov_singleop (operands[0], operands[1],
 				      operands[2], operands[3],
Index: gcc/config/i386/i386.c
===================================================================
--- gcc/config/i386/i386.c	(revision 128981)
+++ gcc/config/i386/i386.c	(working copy)
@@ -15286,6 +15286,13 @@ ix86_expand_movmem (rtx dst, rtx src, rt
       break;
     }
 
+  /* Can't use this if the user has appropriated ecx, esi, or edi.  */
+  if ((alg == rep_prefix_1_byte
+       || alg == rep_prefix_4_byte
+       || alg == rep_prefix_8_byte)
+      && (global_regs[2] || global_regs[4] || global_regs[5]))
+    return 0;
+
   epilogue_size_needed = size_needed;
 
   /* Step 1: Prologue guard.  */
@@ -15594,6 +15601,14 @@ ix86_expand_setmem (rtx dst, rtx count_e
       size_needed = 1;
       break;
     }
+
+  /* Can't use this if the user has appropriated eax, ecx, or edi.  */
+  if ((alg == rep_prefix_1_byte
+       || alg == rep_prefix_4_byte
+       || alg == rep_prefix_8_byte)
+      && (global_regs[0] || global_regs[2] || global_regs[5]))
+    return 0;
+
   epilogue_size_needed = size_needed;
 
   /* Step 1: Prologue guard.  */
@@ -15985,6 +16000,11 @@ ix86_expand_strlen (rtx out, rtx src, rt
   else
     {
       rtx unspec;
+
+      /* Can't use this if the user has appropriated eax, ecx, or edi.  */
+      if (global_regs[0] || global_regs[2] || global_regs[5])
+        return false;
+
       scratch2 = gen_reg_rtx (Pmode);
       scratch3 = gen_reg_rtx (Pmode);
       scratch4 = force_reg (Pmode, constm1_rtx);
Index: gcc/testsuite/gcc.target/i386/pr11001-strlen-2.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr11001-strlen-2.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr11001-strlen-2.c	(revision 0)
@@ -0,0 +1,16 @@
+/* Ensure that we don't use 'repnz scasb' in the presence of register globals.  */
+/* { dg-do compile } */
+/* { dg-options "-O1 -m32" } */
+
+extern __SIZE_TYPE__ strlen (const char *);
+extern void *malloc (__SIZE_TYPE__);
+
+register int regvar asm("%eax"); /* { dg-warning "call-clobbered register" } */
+
+char *
+do_copy (char *str)
+{
+  return malloc (strlen (str) + 1);
+}
+
+/* { dg-final { scan-assembler-not "repnz scasb" } } */
Index: gcc/testsuite/gcc.target/i386/pr11001-memset-2.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr11001-memset-2.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr11001-memset-2.c	(revision 0)
@@ -0,0 +1,23 @@
+/* Ensure that we don't use 'rep stoX' in the presence of register globals.  */
+/* { dg-do compile } */
+/* { dg-options "-Os -m32" } */
+
+extern void *memset (void *, int, __SIZE_TYPE__);
+
+register int regvar asm("%ecx"); /* { dg-warning "call-clobbered register" } */
+
+int foo[10];
+int bar[10];
+
+char baz[15];
+char quux[15];
+
+void
+do_copy ()
+{
+  memset (foo, 0, sizeof foo);
+  memset (baz, 0, sizeof baz);
+}
+
+/* { dg-final { scan-assembler-not "rep stosl" } } */
+/* { dg-final { scan-assembler-not "rep stosb" } } */
Index: gcc/testsuite/gcc.target/i386/pr11001-strlen-3.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr11001-strlen-3.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr11001-strlen-3.c	(revision 0)
@@ -0,0 +1,16 @@
+/* Ensure that we don't use 'repnz scasb' in the presence of register globals.  */
+/* { dg-do compile } */
+/* { dg-options "-O1 -m32" } */
+
+extern __SIZE_TYPE__ strlen (const char *);
+extern void *malloc (__SIZE_TYPE__);
+
+register int regvar asm("%ecx"); /* { dg-warning "call-clobbered register" } */
+
+char *
+do_copy (char *str)
+{
+  return malloc (strlen (str) + 1);
+}
+
+/* { dg-final { scan-assembler-not "repnz scasb" } } */
Index: gcc/testsuite/gcc.target/i386/pr11001-memset-3.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr11001-memset-3.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr11001-memset-3.c	(revision 0)
@@ -0,0 +1,23 @@
+/* Ensure that we don't use 'rep stoX' in the presence of register globals.  */
+/* { dg-do compile } */
+/* { dg-options "-Os -m32" } */
+
+extern void *memset (void *, int, __SIZE_TYPE__);
+
+register int regvar asm("%edi");
+
+int foo[10];
+int bar[10];
+
+char baz[15];
+char quux[15];
+
+void
+do_copy ()
+{
+  memset (foo, 0, sizeof foo);
+  memset (baz, 0, sizeof baz);
+}
+
+/* { dg-final { scan-assembler-not "rep stosl" } } */
+/* { dg-final { scan-assembler-not "rep stosb" } } */
Index: gcc/testsuite/gcc.target/i386/pr11001-memcpy-1.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr11001-memcpy-1.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr11001-memcpy-1.c	(revision 0)
@@ -0,0 +1,23 @@
+/* Ensure that we don't use 'rep movX' in the presence of register globals.  */
+/* { dg-do compile } */
+/* { dg-options "-Os -m32" } */
+
+extern void *memcpy (void *, const void *, __SIZE_TYPE__);
+
+register int regvar asm("%esi");
+
+int foo[10];
+int bar[10];
+
+char baz[15];
+char quux[15];
+
+void
+do_copy ()
+{
+  memcpy (foo, bar, sizeof foo);
+  memcpy (baz, quux, sizeof baz);
+}
+
+/* { dg-final { scan-assembler-not "rep movsl" } } */
+/* { dg-final { scan-assembler-not "rep movsb" } } */
Index: gcc/testsuite/gcc.target/i386/pr11001-memcpy-2.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr11001-memcpy-2.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr11001-memcpy-2.c	(revision 0)
@@ -0,0 +1,23 @@
+/* Ensure that we don't use 'rep movX' in the presence of register globals.  */
+/* { dg-do compile } */
+/* { dg-options "-Os -m32" } */
+
+extern void *memcpy (void *, const void *, __SIZE_TYPE__);
+
+register int regvar asm("%edi");
+
+int foo[10];
+int bar[10];
+
+char baz[15];
+char quux[15];
+
+void
+do_copy ()
+{
+  memcpy (foo, bar, sizeof foo);
+  memcpy (baz, quux, sizeof baz);
+}
+
+/* { dg-final { scan-assembler-not "rep movsl" } } */
+/* { dg-final { scan-assembler-not "rep movsb" } } */
Index: gcc/testsuite/gcc.target/i386/pr11001-memcpy-3.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr11001-memcpy-3.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr11001-memcpy-3.c	(revision 0)
@@ -0,0 +1,23 @@
+/* Ensure that we don't use 'rep movX' in the presence of register globals.  */
+/* { dg-do compile } */
+/* { dg-options "-Os -m32" } */
+
+extern void *memcpy (void *, const void *, __SIZE_TYPE__);
+
+register int regvar asm("%ecx"); /* { dg-warning "call-clobbered register" } */
+
+int foo[10];
+int bar[10];
+
+char baz[15];
+char quux[15];
+
+void
+do_copy ()
+{
+  memcpy (foo, bar, sizeof foo);
+  memcpy (baz, quux, sizeof baz);
+}
+
+/* { dg-final { scan-assembler-not "rep movsl" } } */
+/* { dg-final { scan-assembler-not "rep movsb" } } */
Index: gcc/testsuite/gcc.target/i386/pr11001-strlen-1.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr11001-strlen-1.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr11001-strlen-1.c	(revision 0)
@@ -0,0 +1,16 @@
+/* Ensure that we don't use 'repnz scasb' in the presence of register globals.  */
+/* { dg-do compile } */
+/* { dg-options "-O1 -m32" } */
+
+extern __SIZE_TYPE__ strlen (const char *);
+extern void *malloc (__SIZE_TYPE__);
+
+register int regvar asm("%edi");
+
+char *
+do_copy (char *str)
+{
+  return malloc (strlen (str) + 1);
+}
+
+/* { dg-final { scan-assembler-not "repnz scasb" } } */
Index: gcc/testsuite/gcc.target/i386/pr11001-memset-1.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr11001-memset-1.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/pr11001-memset-1.c	(revision 0)
@@ -0,0 +1,23 @@
+/* Ensure that we don't use 'rep stoX' in the presence of register globals.  */
+/* { dg-do compile } */
+/* { dg-options "-Os -m32" } */
+
+extern void *memset (void *, int, __SIZE_TYPE__);
+
+register int regvar asm("%eax"); /* { dg-warning "call-clobbered register" } */
+
+int foo[10];
+int bar[10];
+
+char baz[15];
+char quux[15];
+
+void
+do_copy ()
+{
+  memset (foo, 0, sizeof foo);
+  memset (baz, 0, sizeof baz);
+}
+
+/* { dg-final { scan-assembler-not "rep stosl" } } */
+/* { dg-final { scan-assembler-not "rep stosb" } } */