[PATCH v3 1/2] perf util: Check for fused instruction

[Jin Yao]

Macro fusion merges two instructions to a single micro-op. Intel
core platform performs this hardware optimization under limited
circumstances.

For example, CMP + JCC can be "fused" and executed /retired
together. While with sampling this can result in the sample
sometimes being on the JCC and sometimes on the CMP.
So for the fused instruction pair, they could be considered
together.

On Nehalem, fused instruction pairs:
cmp/test + jcc.

On other new CPU:
cmp/test/add/sub/and/inc/dec + jcc.

This patch adds an x86-specific function which checks if 2
instructions are in a "fused" pair. For non-x86 arch, the
function is just NULL.

Change-log:
-----------
v3: Add checking for Nehalem (CMP, TEST). For other newer
    Intel CPUs just check it by default (CMP, TEST, ADD,
    SUB, AND, INC, DEC).

v2: Remove the origial weak function. Arnaldo points out
    that doing it as a weak function that will be overridden
    by the host arch doesn't work. So now it's implemented
    as an arch-specific function.

v1: Initial post

Signed-off-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
---
 tools/perf/arch/x86/annotate/instructions.c | 37 +++++++++++++++++++++++++++++
 tools/perf/util/annotate.c                  | 12 ++++++++++
 tools/perf/util/annotate.h                  |  2 ++
 3 files changed, 51 insertions(+)

diff --git a/tools/perf/arch/x86/annotate/instructions.c b/tools/perf/arch/x86/annotate/instructions.c
index c1625f2..8d06dd4 100644
--- a/tools/perf/arch/x86/annotate/instructions.c
+++ b/tools/perf/arch/x86/annotate/instructions.c
@@ -76,3 +76,40 @@ static struct ins x86__instructions[] = {
 	{ .name = "xbeginq",	.ops = &jump_ops, },
 	{ .name = "retq",	.ops = &ret_ops,  },
 };
+
+static bool x86__ins_is_fused(char *cpuid, const char *ins1, const char *ins2)
+{
+	unsigned int family, model, stepping;
+	int ret;
+
+	/*
+	 * cpuid = "GenuineIntel,family,model,stepping"
+	 */
+	ret = sscanf(cpuid, "%*[^,],%u,%u,%u", &family, &model, &stepping);
+
+	if ((ret != 3) || (family != 6) || (model < 0x1e) ||
+	     strstr(ins2, "jmp")) {
+		return false;
+	}
+
+	if (model == 0x1e) {
+		/* Nehalem */
+		if ((strstr(ins1, "cmp") && !strstr(ins1, "xchg")) ||
+		     strstr(ins1, "test")) {
+			return true;
+		}
+	} else {
+		/* Newer platform */
+		if ((strstr(ins1, "cmp") && !strstr(ins1, "xchg")) ||
+		     strstr(ins1, "test") ||
+		     strstr(ins1, "add") ||
+		     strstr(ins1, "sub") ||
+		     strstr(ins1, "and") ||
+		     strstr(ins1, "inc") ||
+		     strstr(ins1, "dec")) {
+			return true;
+		}
+	}
+
+	return false;
+}
diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
index be1caab..8cf6025 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -48,6 +48,8 @@ struct arch {
 	bool		initialized;
 	void		*priv;
 	int		(*init)(struct arch *arch);
+	bool		(*ins_is_fused)(char *cpuid, const char *ins1,
+					const char *ins2);
 	struct		{
 		char comment_char;
 		char skip_functions_char;
@@ -129,6 +131,7 @@ static struct arch architectures[] = {
 		.name = "x86",
 		.instructions = x86__instructions,
 		.nr_instructions = ARRAY_SIZE(x86__instructions),
+		.ins_is_fused = x86__ins_is_fused,
 		.objdump =  {
 			.comment_char = '#',
 		},
@@ -171,6 +174,15 @@ int ins__scnprintf(struct ins *ins, char *bf, size_t size,
 	return ins__raw_scnprintf(ins, bf, size, ops);
 }
 
+bool ins__is_fused(struct arch *arch, char *cpuid, const char *ins1,
+		   const char *ins2)
+{
+	if (!arch || !arch->ins_is_fused || !cpuid)
+		return false;
+
+	return arch->ins_is_fused(cpuid, ins1, ins2);
+}
+
 static int call__parse(struct arch *arch, struct ins_operands *ops, struct map *map)
 {
 	char *endptr, *tok, *name;
diff --git a/tools/perf/util/annotate.h b/tools/perf/util/annotate.h
index 2105503..35cb7b5 100644
--- a/tools/perf/util/annotate.h
+++ b/tools/perf/util/annotate.h
@@ -53,6 +53,8 @@ bool ins__is_jump(const struct ins *ins);
 bool ins__is_call(const struct ins *ins);
 bool ins__is_ret(const struct ins *ins);
 int ins__scnprintf(struct ins *ins, char *bf, size_t size, struct ins_operands *ops);
+bool ins__is_fused(struct arch *arch, char *cpuid, const char *ins1,
+		   const char *ins2);
 
 struct annotation;
 
-- 
2.7.4