https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82405
Bug ID: 82405
Summary: Function not inlined for switch and suboptimal
assembly is generated
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: antoshkka at gmail dot com
Target Milestone: ---
Following code
enum class eShape { eSquare, eCircle, eShpere, eTetraeder };
static inline double eval_square(double r) { return 4 * r*r; }
static inline double eval_circle(double r) { return 3.1415 * r * r; }
static inline double eval_sphere(double r) { return 4 * 3.1415 * r * r; }
static inline double eval_tetraeder(double r) { return 24 * 1.73205 * r*r; }
double test_switch_native(eShape shape, double r) {
switch(shape) {
case eShape::eSquare: return eval_square(r);
case eShape::eCircle: return eval_circle(r);
case eShape::eShpere: return eval_sphere(r);
case eShape::eTetraeder: return eval_tetraeder(r);
}
}
Produces very long suboptimal assembly output with -O2 and -O3.
Clang inlines the functions and merges the common `r*r` part:
test_switch_native(eShape, double): # @test_switch_native(eShape,
double)
movsxd rax, edi
movsd xmm1, qword ptr [8*rax +
.Lswitch.table._Z18test_switch_native6eShaped] # xmm1 = mem[0],zero
mulsd xmm1, xmm0
mulsd xmm0, xmm1
ret
.Lswitch.table._Z18test_switch_native6eShaped:
.quad 4616189618054758400 # double 4
.quad 4614256447914709615 # double 3.1415000000000002
.quad 4623263647169450607 # double 12.566000000000001
.quad 4631047162110439693 # double 41.569200000000002
