cmd/compile/internal/ssa: use sequence of shNadd instructions instead…

… of mul In some cases, we can replace a mul instruction with a sequence of shNadd instructions. Using a sequence of three shNadd instructions does not provide a performance benefit. However, a sequence of two shNadd instructions is still faster than using a single mul instruction. Co-Authored-By: Andrei <[email protected]>
golang · Jan 8, 2025 · ef1cca4 · ef1cca4
1 parent 39f2032
commit ef1cca4
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diff --git a/src/cmd/compile/internal/ssa/_gen/RISCV64.rules b/src/cmd/compile/internal/ssa/_gen/RISCV64.rules
@@ -843,6 +843,24 @@
 (ADD (SLLI [2] x) y) && buildcfg.GORISCV64 >= 22 => (SH2ADD x y)
 (ADD (SLLI [3] x) y) && buildcfg.GORISCV64 >= 22 => (SH3ADD x y)
 
+// Mul on some constants
+(MUL x (MOVDconst [3])) && buildcfg.GORISCV64 >= 22 => (SH1ADD x x)
+(MUL x (MOVDconst [5])) && buildcfg.GORISCV64 >= 22 => (SH2ADD x x)
+(MUL x (MOVDconst [9])) && buildcfg.GORISCV64 >= 22 => (SH3ADD x x)
+
+(MUL <t> x (MOVDconst [11])) && buildcfg.GORISCV64 >= 22 => (SH1ADD (SH2ADD <t> x x) x)
+(MUL <t> x (MOVDconst [13])) && buildcfg.GORISCV64 >= 22 => (SH2ADD (SH1ADD <t> x x) x)
+(MUL <t> x (MOVDconst [19])) && buildcfg.GORISCV64 >= 22 => (SH1ADD (SH3ADD <t> x x) x)
+(MUL <t> x (MOVDconst [21])) && buildcfg.GORISCV64 >= 22 => (SH2ADD (SH2ADD <t> x x) x)
+(MUL <t> x (MOVDconst [25])) && buildcfg.GORISCV64 >= 22 => (SH3ADD (SH1ADD <t> x x) x)
+(MUL <t> x (MOVDconst [27])) && buildcfg.GORISCV64 >= 22 => (SH1ADD (SH3ADD <t> x x) (SH3ADD <t> x x))
+(MUL <t> x (MOVDconst [37])) && buildcfg.GORISCV64 >= 22 => (SH2ADD (SH3ADD <t> x x) x)
+(MUL <t> x (MOVDconst [41])) && buildcfg.GORISCV64 >= 22 => (SH3ADD (SH2ADD <t> x x) x)
+(MUL <t> x (MOVDconst [45])) && buildcfg.GORISCV64 >= 22 => (SH2ADD (SH3ADD <t> x x) (SH3ADD <t> x x))
+(MUL <t> x (MOVDconst [73])) && buildcfg.GORISCV64 >= 22 => (SH3ADD (SH3ADD <t> x x) x)
+(MUL <t> x (MOVDconst [81])) && buildcfg.GORISCV64 >= 22 => (SH3ADD (SH3ADD <t> x x) (SH3ADD <t> x x))
+
+
 // Integer minimum and maximum.
 (Min64  x y) && buildcfg.GORISCV64 >= 22 => (MIN  x y)
 (Max64  x y) && buildcfg.GORISCV64 >= 22 => (MAX  x y)

diff --git a/src/cmd/compile/internal/ssa/rewriteRISCV64.go b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
diff --git a/test/codegen/shift.go b/test/codegen/shift.go
@@ -531,3 +531,26 @@ func checkLeftShiftWithAddition(a int64, b int64) int64 {
 	a = a + b<<3
 	return a
 }
+
+//
+// Multiplication by some constants
+//
+
+func checkMulByConsts(a int64, b int64, c int64, d int64, e int64) (int64, int64, int64, int64, int64) {
+	// riscv64/rva20u64: "MUL"
+	// riscv64/rva22u64: "SH1ADD"
+	a = a * 3
+	// riscv64/rva20u64: "MUL"
+	// riscv64/rva22u64: "SH2ADD"
+	b = b * 5
+	// riscv64/rva20u64: "MUL"
+	// riscv64/rva22u64: "SH2ADD", "SH1ADD"
+	c = c * 13
+	// riscv64/rva20u64: "MUL"
+	// riscv64/rva22u64: "SH1ADD", "SH3ADD"
+	d = d * 27
+	// riscv64/rva20u64: "MUL"
+	// riscv64/rva22u64: "SH3ADD", "SH3ADD"
+	e = e * 73
+	return a, b, c, d, e
+}