This issue is reproducible on latest master.

FS which causes a crash:
#version 430
out vec4 color;
void main()
{
    mat4x3 a;
    a = mat4x3(1.0);
    mat4x3 b;
    b = mat4x3(3.0);
    b *= a;
    color = b[0].xyzz;
}

Just save it as 'test.frag' in piglit folder and execute:
"./bin/glslparsertest test.frag pass 4.30"

You will see an error like:
"ir_swizzle @ 0x5637f74315f0 specifies a channel not present in the value.
 Aborted (core dumped)"

I guess that root cause is because mesa allows such multiplications.
I don't know the reason why mesa allows such multiplication but it should be wrong because of glsl spec is saying "5.9 Expressions":

"The operator is multiply (*), where both operands are matrices or one operand is a vector and the
 other a matrix. A right vector operand is treated as a column vector and a left vector operand as a
 row vector. In all these cases, it is required that the number of columns of the left operand is equal
 to the number of rows of the right operand"

On shader-playground this shader just fails with an error:
'assign' :  cannot convert from ' temp 4X3 matrix of float' to ' temp 4X3 matrix of float'

Note: radv passes this test without errors and crash that also strange)

I am almost done a mesa fix and the piglit test for that.